Bob Ebeling was anxious and angry as he drove to work on the morning of Jan. 28, 1986. He kept thinking about the space shuttle Challenger, cradled on a Florida launchpad 2,000 miles away. Ebeling knew that ice had formed there overnight and that freezing temperatures that morning made it too risky for liftoff.
"He said we are going to have a catastrophic event today," recalled his daughter Leslie Ebeling, who, like her father, worked at NASA contractor Morton Thiokol and who was in the car in 1986 on that 30-mile drive to the company's booster rocket complex outside Brigham City, Utah.
"He said the Challenger's going to blow up. Everyone's going to die. And he was beating his hands on the dashboard. … He was frantic."
The night before, Ebeling and other Morton Thiokol engineers tried to convince NASA, the National Aeronautics and Space Administration, that launching in cold weather could be disastrous. The Thiokol engineers had data, documents and photographs that they believed provided convincing evidence of the risks. And Thiokol executives agreed, at first. Their official recommendation to NASA: Do not launch tomorrow.
What happened next is a story now 40 years old. But it includes critical lessons for the space program that are still relevant today. It has also been a lingering source of guilt for some of the Thiokol engineers who "fought like hell to stop that launch."
"A catastrophe of the highest order"
A problem with Morton Thiokol's booster rocket design emerged during the second shuttle flight in 1981. After that Columbia mission, and after Thiokol's reusable booster rockets were retrieved from their ocean splashdown, an inspection by company engineers showed evidence of "blow-by" in a rocket joint.
The rockets were built in segments, like tin cans stacked on top of each other. Where one segment joined another, two rows of synthetic rubber O-rings were supposed to keep extremely volatile rocket fuel from leaking out. Liftoff and early flight exerted enormous pressure on the rockets, causing the joints to twist apart slightly. The O-rings were supposed to keep those joints sealed. But on that second shuttle flight, searing-hot rocket fuel and gases burned past that inner O-ring barrier in a phenomenon known as blow-by.
Five years and two dozen shuttle missions later, Morton Thiokol had a special task force working full time on O-ring blow-by. One engineer on that task force, Roger Boisjoly, wrote a memo six months before the Challenger disaster that warned of "a catastrophe of the highest order — loss of human life" if the O-ring problem wasn't fixed.
Shuttles continued to launch despite the ongoing risk. Some blame that on something called the "normalization of deviance," a concept coined by sociologist Diane Vaughan in 1996 after she studied the Challenger disaster. Vaughan concluded that even after the risk was identified and even while it was the focus of concern and study, shuttle flights continued because the risk hadn't yet caused a disaster. The "deviance" of the O-ring blow-by became normalized.
A teacher teaching from space
Five days before Challenger's 1986 launch, the shuttle's crew of seven arrived at Kennedy Space Center in Florida, pausing on the tarmac before a gaggle of microphones. Commander Dick Scobee spoke first, followed by pilot Michael Smith, mission specialists Judith Resnik, Ellison Onizuka and Ronald McNair, and payload specialist Gregory Jarvis. The seventh crew member was Christa McAuliffe, a high school teacher from New Hampshire.
"Well, I am so excited to be here," McAuliffe said, smiling broadly. "I don't think any teacher has ever been more ready to have two lessons. … And I just hope everybody tunes in on Day 4 now to watch the teacher teaching in space."
McAuliffe's participation was attracting more attention than usual to shuttle flights at the time. Before this Challenger mission, shuttle launches were so routine that the three major broadcast television networks stopped covering launches live. NASA decided that putting a "teacher in space" aboard would boost interest.
It worked, to a point. The broadcast TV networks didn't carry the launch live, but teachers in classrooms across the U.S. rolled out TV sets so millions of schoolchildren could watch live feeds from CNN or NASA. Busloads of students were also in the crowd at Kennedy Space Center, along with the families of some astronauts.
"It's time to ... put on your management hat"
Bob Ebeling and other company engineers were watching at the Morton Thiokol booster rocket complex in Utah. They crowded into a conference room with Thiokol managers and executives; all focused on a large projection TV screen.
The night before, in the same conference room, Ebeling and his colleagues had tried to convince NASA booster rocket program managers phoning in from the Marshall Space Flight Center in Alabama that the cold weather made launching risky. The synthetic rubber O-rings lining the booster rocket joints stiffened in cold temperatures, and this would be the coldest launch ever by far. The Thiokol engineers feared blow-by would burn through both sets of O-rings, triggering an explosion at liftoff.
At first, Thiokol's engineers and executives officially recommended a launch delay. But the NASA officials on the line pushed back hard. The launch had already been delayed five times. The NASA officials said the engineers couldn't prove the O-rings would fail. One of those engineers, looking back on it now, 40 years later, says it was an unachievable burden of proof.
"It's impossible to prove that it's unsafe. Essentially, you have to show that it's going to fail," explains Brian Russell, who was a program manager at Morton Thiokol in 1986 and who was focused on the O-rings and booster rocket joints.
"What we were saying was we're increasing the risk significantly," Russell recalls. But "you just can't" prove the O-rings will fail, he adds. "So, we were in an absolute lose situation."
NASA's resistance during the contentious, sometimes argumentative conference call eventually wore down the four Thiokol executives in the Utah conference room. They and the NASA officials on the line also heard one piece of data that fed their resistance. O-ring blow-by had also occurred during a warm launch: 75 degrees.
"So, it wasn't just as easy as saying, 'Hey, we were on a rock-solid foundation with no opposing data.' We weren't," Russell remembers. Russell also says the data showed that damage at colder temperatures was far more severe and alarming.
Thiokol had a lot at stake with this Challenger launch. The company's contract with NASA imposed a $10 million penalty for a launch delay due to the booster rockets. That contract was worth $800 million, and it was up for renewal in 1986.
The Thiokol executives put NASA on hold so they could speak privately with their engineers. Russell, Ebeling, Boisjoly and another engineer in the room were insistent. It was too risky to launch, they said. Finally, Thiokol Senior Vice President Jerry Mason polled the company executives. He and two others quickly agreed to reverse their earlier recommendation and approve the launch. Mason then turned to Bob Lund, the vice president in charge of engineering.
"And Bob hesitated and hummed and hawed, and I could tell it was such a difficult decision for him, and it was all hinging on him," Russell recalls. "He was representing both management as well as engineering … and in his hesitation, Jerry Mason said, 'Bob, it's time to take off your engineering hat and put on your management hat.'"
And that's precisely what Lund did. He put on his management hat and voted to overrule his engineers. Challenger's fate was set.
A major malfunction
The next morning, NASA's live feed showing launch preparations included this announcement from the launch control team: "I have polled the technical community, and you have our consensus to proceed with this launch. Good luck and Godspeed."
Brian Russell, Bob Ebeling and Roger Boisjoly knew that wasn't true. They were part of the "technical community," and they never backed down from their recommendation to delay. But the launch director and other top NASA officials didn't know it. All they knew was what the lower-level officials at the Marshall Space Flight Center told them: Thiokol and its rockets were "go" for launch. At the time, that's all that was expected. The Marshall Space Flight Center supervised Thiokol's booster rockets, and the Marshall officials simply told the launch control team that the boosters were ready.
Leslie Ebeling watched the launch with her dad and the other engineers in the Thiokol conference room. The elder Ebeling and a few others expected a disastrous explosion at ignition. So when Challenger lifted off and cleared the launch tower, there was some relief. But not for Bob Ebeling.
"My dad bent down to tell me that it wasn't over yet, that things weren't clear. And I could feel him trembling," recalled Leslie Ebeling. Then launch control announced, "Challenger, go with throttle up."
Suddenly, there was a moment of static on the audio feed, along with billowing smoke and flames in the video, as well as pieces of the spacecraft shooting wildly across the sky. "Obviously a major malfunction," said a voice on the NASA feed.
"And then he wept, loudly," Leslie Ebeling said of her dad's response. "And the silence in that room was deafening. There was no one talking. It was just dead silence."
In the crowd at Kennedy Space Center, a TV camera and microphone captured screams and sobbing, and the faces of Christa McAuliffe's parents as they looked skyward in anguish. A loudspeaker with the NASA feed confirmed the worst: "We have a report relayed through the Flight Dynamics Office that the vehicle has exploded."
That night, CBS News anchor Dan Rather called it "the worst disaster in the U.S. space program ever."
"Tonight, the search for survivors turned up none," Rather continued. "The search for answers is just starting."
"I fought like hell to stop that launch"
A special presidential commission began investigating a week after the tragedy but initially failed to get the full story from NASA witnesses. At the first public hearing, on Feb. 6, Judson Lovingood, a shuttle manager at NASA's Marshall Space Flight Center, provided a truncated description of the conference call with Thiokol.
"We had the project managers from both Marshall and Thiokol in the discussion," Lovingood testified. "We had the chief engineers from both places in the discussion. And Thiokol recommended to proceed in the launch."
Lovingood added that there was some concern about the cold temperatures in the forecast, but that's all he said. There was no mention of the objections of the Thiokol engineers, so the commission moved on.
Four days later, in a hearing behind closed doors, Lawrence Mulloy, another top official at Marshall, said, "We all concluded that there was no problem with the predicted temperatures."
But this time, one of the Thiokol engineers was in the room.
"I was sitting there thinking, 'Well, I guess that's true, but that's about as deceiving as anything I ever heard,'" recalled Allan McDonald in a 2016 interview. He was the immediate supervisor of the Thiokol engineers.
McDonald was sitting in the back of the room, in what he called the cheap seats, and unable to restrain himself, he spoke up.
"I think this presidential commission should know that Morton Thiokol was so concerned, we recommended not launching below 53 degrees Fahrenheit, and we put that in writing and sent that to NASA," McDonald remembers saying.
"I'll never forget Chairman William Rogers and his vice chairman, Neil Armstrong, standing up and squinting and looking at me, and Chairman Rogers said, 'Would you please come down here on the floor and repeat what I think I heard?'"
The forecast for overnight temperatures for the Challenger launch ranged from 18 to 26 degrees Fahrenheit. The air temperature was still only 36 degrees after a two-hour launch delay.
Four days later, in another closed-door hearing, the commission heard the first formal testimony from Thiokol engineers. McDonald told the commission that Thiokol was pressured by NASA to approve the launch. Roger Boisjoly, who led the eleventh-hour effort to delay the launch, testified about the O-ring task force, including his warning of a catastrophe six months before.
Little of this testimony was public. Bits of closed-door testimony leaked, but not the dramatic details of the decision-making process that failed to heed dire warnings of a disaster. Those details were finally revealed on Feb. 20, 1986, in a pair of stories for NPR's Morning Edition, reported by my colleague Daniel Zwerdling and me.
We managed to get two Thiokol engineers to provide a play-by-play account of the conference call the night before the launch, including direct quotes. Both engineers remained anonymous at the time. They feared for their jobs, and they'd been ordered by Thiokol not to talk publicly about the incident. They also declined to be recorded. But they allowed us to report what they said. Decades later, NPR was permitted to publicly identify them both.
"I fought like hell to stop that launch," a tearful Boisjoly told Zwerdling in a hotel room near the Marshall Space Flight Center in Huntsville, Ala., on Feb. 19, three weeks after the explosion. "I'm so torn up inside I can hardly talk about it, even now."
"I should have done more"
At the same time, 1,700 miles away in Brigham City, Utah, Bob Ebeling spoke with me. He was still frantic, pacing back and forth between his kitchen and living room, shaking his head and wringing his hands.
Both Ebeling and Boisjoly provided identical stories about that conference call.
When the Thiokol engineers argued that NASA should wait for warmer weather, Marshall's Lawrence Mulloy blurted out, according to Ebeling, "My God, Thiokol, when do you want me to launch, next April?"
NASA was trying to prove the space shuttle could fly on a regular and reliable schedule, and in every month of the year, despite cold weather. Mulloy later told the Challenger commission that he didn't believe he was applying pressure that night before the launch.
"Any time that one of my contractors … who come to me with a recommendation and a conclusion that is based on engineering data, I probe the basis for their conclusion to assure that it is sound and that it is logical," Mulloy testified.
But Mulloy's comment, which he did not deny making, proved pivotal. It preceded the decision of the Thiokol executives to overrule their engineers.
Ebeling told me that he saw in the local newspaper a photo of graffiti on a railroad overpass that said, "Morton Thiokol Murderers." He then walked into the living room, where haunting images of the Challenger explosion appeared in a TV news report.
"I should have done more," Ebeling then said. "I could have done more."
Lessons learned
The Challenger commission concluded it was "an accident rooted in history," given the evidence of O-ring damage before the fatal launch and the failure to heed the warnings of the Thiokol engineers.
The commission also documented a shocking gap in the Challenger launch decision: the failure of the lower-level officials at the Marshall Space Flight Center to tell the launch control team that there were serious concerns about launching. At a hearing on Feb. 27, Commission Chairman William Rogers posed a key question to the Challenger launch director, the Kennedy Space Center director and two top shuttle program executives.
"Did any of you gentlemen prior to launch know about the objections of Thiokol to the launch?" Rogers asked. Each of the four top NASA launch officials responded with a "No, sir" or "I did not."
"Certainly, four of the key people who made the decision about the launch were not aware of the history we've been unfolding here before the commission," Rogers concluded.
NASA changed the launch decision process after the Challenger disaster so that objections of contractors would reach the launch control team.
But, still, 17 years later, after another shuttle, Columbia, disintegrated during its Earth reentry, a NASA investigation blamed, in part, "organizational barriers that prevented effective communication of critical safety information and stifled professional differences of opinion."
Columbia and Challenger prompted NASA, as well as one of the Thiokol engineers, to systematically remind space agency officials, workers and contractors about key lessons from Challenger and other disasters.
The lessons from Challenger are critical for "the next generation of spaceflight," said Michael Ciannilli recently, who retired from NASA after 36 years at the space agency, including in a key role in launch decisions after Challenger. Ciannilli also developed and implemented an "Apollo, Challenger, Columbia Lessons Learned Program" at NASA, which has involved thousands of NASA employees and contractors.
"The folks in the organizations have to feel it's not just platitudes or a nice slogan. But that's really how it is. … We honor dissenting opinion. We welcome dissenting opinion. There's no ramifications," Ciannilli says.
He left NASA as the agency shed 4,000 workers last year, but he says he'll continue his "lessons learned" work as a contractor.
NASA also invited me to speak about my reporting on Challenger to project and safety managers at the agency's Goddard Space Flight Center and the Langley Research Center in 2017. My assigned topic: "Listening to Dissent."
Former Thiokol engineer Brian Russell has been taking a similar message to mission management teams and other NASA officials at the Johnson Space Center, Kennedy Space Center, NASA headquarters and the Marshall Space Flight Center (twice) — all since April 2025.
"The people that are involved in the programs today face the same issues. They face the same pressures when it comes to wanting to launch," Russell explains.
"They're going to be under the pressure to perform, and no one wants to be the one to stand up and say, 'I'm not ready,'" he continues. "But the listening under high-stress environments like that is really crucial, and that's the crux of our message."
"You have to have an end to everything"
Still, Russell has some lingering regret about his role in the effort to stop the Challenger launch. He recalls the moment in 1986 when the Thiokol executives overruled the engineers, reconnected the conference call and told the NASA officials that Thiokol was "go" for launch.
"The thing that I feel the most guilt over … [is] I wish I'd have said, 'There's a dissenting view here.' I wish the [NASA] people on the phone call would've heard that," Russell says, his eyes filling with tears. "But I still didn't speak up. So, I regret that … to this day."
Roger Boisjoly told me in an interview in 1987 that he had no regrets. "There's nothing I could have done further because you have to realize we were talking to the right people. … We were talking to the people that had the power to stop the launch."
Boisjoly blamed Thiokol and NASA. He later became a leading voice for ethical decision-making in the engineering and leadership worlds. Boisjoly died in 2012.
Allan McDonald, the engineer who first spoke out during an early Challenger commission hearing, was initially demoted and sidelined by Thiokol. But members of Congress vowed to make sure the company would never receive another NASA contract if it punished McDonald and the other engineers for speaking out. Thiokol relented, and McDonald was put in charge of the successful redesign of the booster rocket joints. "That turned out to be the best therapy in the world," he told me in 2016. McDonald died in 2021.
Bob Ebeling carried deep and painful guilt for 30 years. In 2016, he told me that putting him on that conference call with NASA the night before the launch was "one of the mistakes that God made." It was something he prayed about.
"[God] 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.'"
Ebeling was 89 then and had home hospice care. He used parallel bars to walk from his kitchen table to his favorite easy chair in the living room.
I reported his painful regret in a story on the 30th anniversary of the Challenger disaster, and hundreds of NPR listeners responded, including all kinds of engineers. Most had comforting words. Two of the key people who were involved in the 1986 conference call, and who did not heed the warnings of the engineers, also responded, saying Ebeling provided data and documents. They told him that he did his job and was not the decision-maker, so he should not bear any blame.
NASA also responded with a statement, which I read to Ebeling in February 2016: "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."
Hearing that, Ebeling smiled, raised his hands above his head and clapped. "Bravo! I've had that thought many times," he said.
"You have to have an end to everything," he added before I left, as he clapped and smiled again.
Bob Ebeling died three weeks later, at peace, his family said.
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