NPR’s Two-Way blog remembers Roger Boisjoly, the Morton Thiokol booster rocket engineer who wrote a report six months before the Space Shuttle Challenger explosion warning about the danger of launching in cold weather. He died last month in Utah at age 73.

Boisjoly was disturbed about data showing the elastic seals at the joints of the multistage shuttle booster rockets tended to stiffen and unseal when cold, and wrote a memo to managers predicting “a catastrophe of the highest order” involving “loss of human life.” On Jan. 27, 1986, he and four colleagues concluded it would be too risky to launch Challenger the next morning given the frigid weather.

After the shuttle broke apart 73 seconds into its flight, killing all seven crew members, Boisjoly met with NPR’s Daniel Zwerdling for a confidential interview. “I fought like hell to stop that launch,” he said.

“I’m so torn up inside I can hardly talk about it, even now.”