When NPR reported Bob Ebeling's story on the 30th anniversary of the explosion of the space shuttle Challenger, hundreds of listeners and readers expressed distress and sympathy in letters and emails.

On Jan. 27, 1986, the former engineer for shuttle contractor Morton Thiokol had joined four colleagues in trying to keep Challenger grounded. They argued for hours that the launch the next morning would be the coldest ever. Freezing temperatures, their data showed, stiffened rubber O-rings that keep burning rocket fuel from leaking out of the joints in the shuttle's boosters.

But NASA officials rejected that data, and Thiokol executives overruled Ebeling and the other engineers.

"It's going to blow up," a distraught and defeated Ebeling told his wife, Darlene, when he arrived home that night.

And it did, 73 seconds after liftoff. Seven astronauts died. Cold weather and an O-ring failure were blamed, and Ebeling carried three decades of guilt.

"That was one of the mistakes God made," Ebeling, now 89, told me three weeks ago at his home in Brigham City, Utah. "He shouldn't have picked me for that job. But next time I talk to him, I'm gonna ask him, 'Why me? You picked a loser.' "

Jim Sides listened to the NPR story in his car in Jacksonville, N.C.

"When I heard he carried a burden of guilt for 30 years, it broke my heart," Sides, an engineer, says. "And I just sat there in the car in the parking lot and cried."

Like many engineers who responded to Ebeling's story, Sides knows what it's like to present data and face resistance. He's also certain about who bears responsibility for the decisions that result.

"He and his colleagues stated it very plainly. It was a dangerous day for the launch," Sides says. "But [Ebeling] was not the decision-maker. He did his job as an engineer. He should not have to carry any guilt."

Sides wrote Ebeling a letter that mentioned Roger Boisjoly, a former Thiokol colleague who died in 2012 and rallied the engineers opposing the Challenger launch. Boisjoly addressed his own depression and guilt by making the Challenger experience a case study in ethical decision-making.

Many of the engineers who also wrote Ebeling credited him and Boisjoly for engineering school discussions that focused on the Challenger decision.

"Your efforts show that your care for people comes first for you," Sides wrote to Ebeling. "I agree with your friend Roger Boisjoly. You and he and your colleagues did all that you could do."

Sides describes himself as a religious man and says Ebeling was wrong about God.

"God didn't pick a loser," he says. "He picked Bob Ebeling."

Ebeling's eyesight is so poor he can't read the letters himself. So his daughter Kathy read them aloud, including the note from Sides.

"That's easy to say," Ebeling responded. "But after hearing that, I still have that guilt right here," he said pointing to his heart.

This was a week after the Challenger anniversary story, and Ebeling sat in a wheelchair at his kitchen table, wearing a flannel shirt and pajamas. Letters and printed emails were stacked in front of him. Kathy picked another letter from the pile and tried again.

"You presented the correct data and blew the whistle," another listener wrote. "You are not a loser. You are a challenger."

Again, Ebeling wasn't moved. So I asked him if there's something more he wanted to hear.

"You aren't NASA. You aren't Thiokol," he said. "I hadn't heard any of those people."

Kathy noted that neither Thiokol nor NASA had contacted her dad since deep depression prompted his retirement shortly after the Challenger disaster.

"He's never gotten confirmation that he did do his job and he was a good worker and he told the truth," Kathy said.

Thiokol has since been absorbed by another company. There isn't anyone there or at NASA today who was likely involved in the launch decision.

But some retired participants in that decision are still alive, including 78-year-old Allan McDonald, who was Ebeling's boss at the time and a leader of the effort to postpone the launch. He called Ebeling right away.

McDonald told Ebeling that his definition of a loser is "somebody that really doesn't do anything. But worse yet, they don't care. I said, 'You did something and you really cared. That's the definition of a winner.' "

McDonald also reminded Ebeling that he first raised the alarm by calling the Kennedy Space Center, where McDonald was Thiokol's launch representative. That call prompted the 11th-hour teleconference in which the engineers told NASA it was too risky to launch.

"If you hadn't have called me," McDonald told Ebeling, "they were in such a go mode, we'd have never even had a chance to try to stop it."

McDonald also responded to some NPR listeners who were not sympathetic to Ebeling and the other Thiokol engineers. They said the engineers should have done more, including last-ditch calls to NASA's launch director or even the White House.

"You just don't do that," McDonald said. "They'd probably send a van out with some white coats and picked you up. ... The launch director doesn't take those outside calls either."

Another key participant in the launch decision was Robert Lund, who was Thiokol's vice president for engineering at the time. He was one of the company executives who approved the Challenger launch despite objections from Ebeling, Boisjoly, McDonald and others.

Lund wouldn't agree to a recorded interview, saying, "I don't want to relive it." He was reassigned by Thiokol and so "shamed by the neighbors" that his family was forced to move, he said. "It was a bad dream."

But Lund said he phoned Ebeling and told him, "You did all that you could do."

A former NASA official involved in the Challenger launch also declined to be interviewed. George Hardy was a deputy director of engineering at the Marshall Spaceflight Center, which supervised Thiokol's production of the shuttle's booster rockets. He famously said he was "appalled" when Ebeling and the other engineers argued that Challenger shouldn't fly in temperatures so cold.

Hardy now says he's gone over that night many times.

"I've concluded that's of no great value to me or anyone else," he said.

But he did see value in writing to Ebeling.

"You and your colleagues did everything that was expected of you," Hardy wrote. "The decision was a collective decision made by several NASA and Thiokol individuals. You should not torture yourself with any assumed blame."

Hardy closed with a promise to pray for Ebeling's physical and emotional health. "God bless you," he wrote.

The note from Hardy and the phone call from McDonald seemed to be a turning point. It was two weeks now after the Challenger story, and Kathy had been reading letter after letter every day. Sitting in his big easy chair in his living room, Ebeling's eyes and mood seemed brighter.

"I've seen a real change," his daughter explained. "He doesn't have a heavy heart like he did."

Ebeling then jumped in.

"I know that is the truth that my burden has been reduced," he said. "I can't say it's totally gone, but I can certainly say it's reduced."

The night before, NASA had sent a statement and Ebeling hadn't heard it yet. The statement was emailed by a spokeswoman for NASA Administrator Charlie Bolden, a former astronaut. He flew on the shuttle flight just before Challenger, and later led the effort to resume shuttle flights safely.

"We honor [the Challenger astronauts] not through bearing the burden of their loss, but by constantly reminding each other to remain vigilant," the statement read. "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."

After hearing that, Ebeling clapped long and hard, and shouted, "Bravo!"

"I've had that thought many, many times," he said.

Ebeling is now more buoyant than at any time I've seen or talked to him in the past 30 years. It's been a rough three decades, and it hasn't gotten any easier. He's near the end of his predicted life expectancy for prostate cancer and has hospice care at home. He said he'll pray for God's assessment once our interview ends.

I asked him one more question. "What would you like to say to all the people who have written you?"

"Thank you," he said. "You helped bring my worrisome mind to ease. You have to have an end to everything."

Ebeling then smiled, raised his hands above his head and clapped again. Kathy Ebeling called that a miracle.



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AUDIE CORNISH, HOST:

Hundreds of NPR listeners responded after hearing a story we aired last month about the 30th anniversary of the space shuttle Challenger explosion in which the seven astronauts died. The story featured 89-year-old Bob Ebeling. He was an engineer for NASA contractor Morton Thiokol. He tried to stop the Challenger launch, and his failure to do that, he told us, continues to haunt him.

(SOUNDBITE OF ARCHIVED BROADCAST)

BOB EBELING: And I think that was one of the mistakes that God made. He shouldn't have picked me for that job. I don't know. But next time I talk to him, I'm going to ask him, why me? You picked a loser.

CORNISH: We wanted to know if your letters and emails made him think differently about his role in that tragedy. So NPR's Howard Berkes returned to Ebeling's home in Utah to find out.

HOWARD BERKES, BYLINE: A week after our story aired, with snow falling in Brigham City, Utah, I barely got in the door before Bob Ebeling declared nothing had changed.

B. EBELING: I still have this guilt complex.

DARLENE EBELING: (Laughter).

BERKES: That's his wife, Darlene, chuckling and shaking her head. Letters seeking to comfort Ebeling lay unfolded on the kitchen table. They hadn't made much difference. His prayers hadn't either.

B. EBELING: And I hope that he can forgive me for not being better than I was.

BERKES: This is the sentiment that compelled so many people to write, including 51-year-old Jim Sides, who sat in his car in Jacksonville, N.C., listening to the radio, mesmerized by Ebeling's words.

JIM SIDES: And when I had heard he'd carried a burden of guilt for 30 years, it broke my heart, and I just - I sat there in the car in the parking lot and cried.

BERKES: Sides is a utility engineer, and he thought about Ebeling's mission, as he calls it, the night before Challenger was launched. Ebeling and other Thiokol engineers had data that showed the risk. Rubber O-rings that seal the joints in the shuttle's booster rockets can fail to seal in cold weather. Leaking rocket fuel could then cause an explosion, and this would be the coldest launch yet.

SIDES: He and his colleague stated it very plainly. It was a dangerous day for the launch. But he was not the decision-maker. He did his job as an engineer. He should not have to carry any guilt.

BERKES: Other engineers wrote to Ebeling, saying they learned about the Challenger launch decision in engineering school. It's a case study in ethical decision-making. They credit Ebeling for that, along with Roger doubling for that along with Roger Boisjoly, who died in 2012 and also fought the launch. Sides mentions Boisjoly in his letter to Ebeling.

SIDES: Your efforts show that your care for people comes first for you. I agree with your friend, Roger Boisjoly...

KATHY EBELING: I agree with your friend, Roger Boisjoly. You and he and your colleagues did all that you could do.

B. EBELING: That's easy to say, but after hearing that, I still have that guilt right here.

BERKES: Ebeling points to his heart. He sits in a flannel shirt and pajama bottoms in a wheelchair at his kitchen table. Kathy picks another letter from the pile and tries again.

K. EBELING: You presented the correct data and blew the whistle. You did everything you could, and I hope this letter helps you. You are not a loser. You are a challenger. God bless you.

BERKES: We're interrupted by a Meals on Wheels delivery, and as Kathy grabs the bags of food, I ask her dad if there's something more he wants to hear.

B. EBELING: You aren't NASA. You aren't Thiokol. I haven't heard any of those people.

K. EBELING: He's never gotten confirmation that he did do his job and he was a good worker and he told the truth.

BERKES: There isn't anyone still at NASA or the company that absorbed Thiokol who was likely involved in the launch decision, but some retired participants are still alive. So I started tracking them down, beginning with 78-year-old Allan McDonald, Ebeling's boss at the time and a leader of the effort to keep Challenger on the ground. He responded right away.

ALLAN MCDONALD: I called him 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. I said, you did something, and you really cared. That's the definition of a winner.

BERKES: McDonald says Ebeling first raised the alarm by calling the Kennedy Space Center where McDonald was Thiokol's launch representative. That call prompted the 11th-hour teleconference in which the engineers told NASA it was too risky to launch.

MCDONALD: And I said, think about this, Bob. If you hadn't have called me, they were in such a go-mode, we would have never even had a chance to try to stop it.

BERKES: McDonald also responds to the NPR listeners who are not sympathetic to Ebeling and the other engineers. They should've done more, those listeners wrote; the engineers should have phoned NASA's launch director or the White House.

MCDONALD: They'd probably send a van out with some white jackets and picked you up, first of all. You just don't do that. The launch director doesn't take those outside telephone calls either.

BERKES: Another key player in the launch decision didn't want to be interviewed. George Hardy is 85 now and was a NASA deputy director in 1986. He famously said he was appalled when Ebeling and the other engineers said Challenger shouldn't fly. Hardy said he'd gone over that night many, many times. There was no great value, he said, in continuing to review it. He did see value, though, in writing to Ebeling.

Do you remember George Hardy from NASA?

B. EBELING: Yes.

BERKES: He said you and your colleagues did everything that was expected of you. The decision was a collective decision made by several NASA and Thiokol individuals. You should not torture yourself with any assumed blame.

B. EBELING: Thank you.

BERKES: Hearing from Hardy and McDonald seemed to be a turning point which came two weeks after the story aired. Ebeling sat in his big easy chair in the living room, his eyes and mood brighter.

K. EBELING: I've seen a change, a real change. He doesn't have a heavy heart like he did.

B. EBELING: And I know that there's a truth that my burden has been reduced. I can't say it's totally gone, but I can certainly say it's been reduced.

BERKES: I also read aloud a statement Ebeling had yet to hear. It was emailed the night before by a spokeswoman for NASA administrator Charlie Bolden. a former astronaut who led the effort to resume shuttle flights safely after Challenger.

So this is a statement from NASA. So they're talking about the astronauts. We honor them 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.

(APPLAUSE)

B. EBELING: Bravo. I've had that same thought many, many times.

BERKES: Ebeling is now more buoyant than at any time I've seen or talked to him in the last 30 years despite cancer and hospice care. He'll pray again for God's assessment, he says, when our interview ends. I ask one more question. Is there anything he'd like to say to the people who wrote to him?

B. EBELING: Thank you. You helped bring my worrisome mind to ease. You have to have an end to everything.

BERKES: And as I leave, Bob Ebeling smiles, raises his hands above his head and claps. Kathy Ebeling calls that a miracle. Howard Berkes, NPR News.

CORNISH: And we've posted a statement from the Ebeling family to NPR listeners at npr.org. Transcript provided by NPR, Copyright NPR.