WASHINGTON — ‘‘Why me?’’

This is what Bob Ebeling planned to demand of God, when he saw him: ‘‘Why me? You picked a loser.’’

For three decades Mr. Ebeling, a former rocket engineer for NASA contractor Morton Thiokol, had been swamped by his own grief and guilt over the catastrophe he’d failed to stop. In the days before the space shuttle Challenger burned up in mid-air, killing all seven astronauts on board, Mr. Ebeling and four other engineers had pleaded with NASA to delay the launch. They had concerns about whether the rubber o-rings on the shuttle’s booster rockets would seal properly in the frigid winter weather. Mr. Ebeling even authored an alarmed memo detailing the problems with the rings. Its subject line read, bluntly, ‘‘Help!’’

But the engineers were overruled. On Jan. 28, 1986, he and his colleagues watched in helpless horror as the shuttle and its crew turned to ashes in the sky.

‘‘I think that was one of the mistakes that God made,’’ Mr. Ebeling told NPR this year. ‘‘He shouldn’t have picked me for that job. I don’t know.’’

But hundreds of people who listened to that interview, which aired on the 30th anniversary of the Challenger explosion in January, disagreed. They included Allan McDonald, Mr. Ebeling’s boss and Thiokol’s representative at the Kennedy Space Center in Florida on the day of the launch.

‘‘I called up and told him, ‘You know, to me, my definition of a loser is somebody that really doesn’t do anything, but worse yet, they don’t care,’?’’ McDonald told NPR a month later. ‘‘I said, ‘You did something, and you really cared. That’s the definition of a winner.’?’’

Mr. Ebeling died Monday in Brigham City, Utah, at age 89, his family said. But, thanks in part to the assurances from McDonald and untold others, he goes to God less burdened by the question that has haunted him for the past 30 years.

‘‘It was as if he got permission from the world,’’ his daughter Leslie Ebeling Serna told NPR. ‘‘He was able to let that part of his life go.’’

Mr. Ebeling leaves his wife, Darlene, and 35 descendants spanning four generations.

The Illinois native had lived in Brigham City for more than a half-century. He was a quiet, prayerful man — a husband, a devoted father, a great lover of the outdoors. He spent his free time birding, biking, and boating in the vast wetland not too far from the Thiokol plant where he worked, he told the Salt Lake Tribune.

But he knew sorrow, too. In the years before the Challenger explosion, his son had committed suicide, Mr. Ebeling told the Los Angeles Times in 1987. At the time, Mr. Ebeling had cradled the young man in his arms and wondered why he hadn’t done more to prevent his death.

It was a question he’d soon be asking himself again.

In 1985, booster rockets recovered from the Jan. 24 launch of the shuttle Discovery showed signs of seal problems. Mr. Ebeling, who had been working in engineering for 40 years, and two other engineers were assigned to examine the issue. Their findings were worrying — the rubber o-ring seals stiffened in cold weather, allowing the hot, high pressure gas inside the boosters to leak out — but NASA and their managers at Thiokol were slow to react.

That October, Mr. Ebeling wrote an urgent memo to McDonald, his boss, under the now-infamous subject line ‘‘Help!’’ He told McDonald that the rocket seal task force needed more resources, according to a presidential commission’s 1986 report on the accident, and signed off with the words ‘‘This is a red flag.’’

But the launch date, already delayed once because of wind conditions, was approaching, with forecasted temperatures of about 30 degrees. The afternoon before the Challenger was due to take off, Mr. Ebeling called McDonald warning him that the cold could be disastrous for the launch. That set off six hours of teleconferences between Thiokol engineers and executives and officials with NASA. Mr. Ebeling wasn’t on that phone call, according to the Times — but McDonald, along with engineers Arnold Thompson and Roger Boisjoly, argued emphatically for a delay.

The space agency was determined to launch, though it’s never been quite clear why. President Reagan was due to discuss the space program in his State of the Union address that night. NASA also prided itself on sending up shuttles routinely and reliably, and it had already pushed back the Challenger launch once.

Either way, officials fiercely resisted the suggestion of another delay.

Mr. Ebeling drove home uncharacteristically furious. ‘‘It’s going to blow up,’’ he told his wife, grimly.

The next day, Mr. Ebeling invited Boisjoly, his fellow engineer, into his office to watch the shuttle take off. When the clock reached T minus 5 seconds, Boisjoly would later tell the Guardian, the two men reached out to hold each other’s hands.

Three. Two. One.

At ‘‘lift off,’’ the shuttle rocketed into the sky, clearing the launch pad without issue.

‘‘I turned to Bob and said, ‘We’ve dodged a bullet,’?’’ Boisjoly recalled.

Mr. Ebeling, meanwhile, was in the midst of a prayer: ‘‘Thank you for making me wrong,’’ he whispered. And then: ‘‘Kaboom. It went,’’ Mr. Ebeling told CBS. ‘‘I — I walked right out of there and went in my office and cried.’’

All seven astronauts on board died: commander Francis Scobee, pilot Michael Smith, mission specialist Ellison Onizuka, mission specialist Judith Resnik, mission specialist Ronald McNair, payload specialist Gregory Jarvis, and ‘‘teacher in space’’ Christa McAuliffe.

Three weeks later, Mr. Ebeling and Boisjoly agreed to anonymous interviews with NPR in which they detailed their failed fight to stop the launch. It was the first report that NASA knew what could happen.

‘‘I should have done more,’’ Mr. Ebeling told reporter Howard Berkes at the time. ‘‘I could have done more.’’

He, Boisjoly, McDonald, Thompson, and a fifth engineer, Brian Russell, would later give testimony before the presidential commission investigating the explosion. All of them said the same thing: NASA and Thiokol had been warned that it was unsafe to launch in the cold, but they went ahead anyway.

Within the company, the men who testified about Thiokol and NASA’s failures became known as ‘‘the five lepers,’’ according to the Los Angeles Times. Resentment from those at the company who hoped to avoid official blame — or were simply terrified for their jobs — compounded the engineers’ agony over their inability to prevent the explosion. The ‘‘lepers’’ were isolated at meetings, excluded from technical conferences; their reports were routinely ignored.

Eventually, Mr. Ebeling retired. He felt like he ‘‘wasn’t needed anymore’’ at his job, he told the Times, and to be honest, he wanted nothing to do with the shuttle program any more.

When Berkes, the NPR reporter who had interviewed him 1986, approached him again for the disaster’s 30th anniversary, Mr. Ebeling was no less hard on himself than he’d been in the three weeks after Challenger fell from the sky.

He was inadequate, he told Berkes. He didn’t argue the data well enough. Maybe another man would have been able to convince NASA to delay, but not him. He was, as he planned to tell God, ‘‘a loser.’’

The story elicited strong empathy from throughout the scientific community, including those who were with NASA at the time of the liftoff. A statement from current NASA administrator Charlie Bolden said: ‘‘We honor [the Challenger astronauts] not through bearing the burden of their loss, but by constantly reminding each other to remain vigilant. And to listen to those like Mr. Ebeling who have the courage to speak up so that our astronauts can safely carry out their missions.’’

The statement made Mr. Ebeling clap. Despite having to use a wheelchair and sick with prostate cancer, Berkes reported that 89-year-old was in brighter spirits than any time he’d seen him in the last 30 years.

‘‘It’s wonderful, it’s like a miracle,’’ Mr. Ebeling’s daughter Kathy said last month. ‘‘It’s starting to change his mind that he doesn’t feel so guilty, so that’s a miracle. Thirty years of guilt is long enough.’’