Six months before the space shuttle Challenger exploded over Florida on Jan. 28, 1986, Roger Boisjoly wrote a portentous memo. He warned that if the weather was too cold, seals connecting sections of the shuttle’s huge rocket boosters could fail.

“The result could be a catastrophe of the highest order, loss of human life,” he wrote.

The memo was meant to jolt Morton Thiokol, the company that made the boosters and employed Mr. Boisjoly. In July 1985, a task force had been formed, partly on Mr. Boisjoly’s recommendation, to examine the effect of cold on the boosters. The effort, however, had become mired in paperwork, procurement delays and a rush to launch the shuttle, according to later investigations.

Meanwhile, his apprehensions only grew. The night before the Challenger’s liftoff, the temperature dipped below freezing. Unusual for Florida, the cold was unprecedented for a shuttle launching, and it prompted Mr. Boisjoly and other engineers to plead that the flight be postponed. Their bosses, under pressure from NASA, rejected the advice.

The shuttle exploded 73 seconds after launching, killing its seven crew members, including Christa McAuliffe, a high school teacher from Concord, N.H.