Roger Boisjoly

Six months before the space shuttle Challenger exploded on Jan. 28, 1986, Roger Boisjoly wrote a portentous memo, warning that if the weather were too cold, seals connecting sections of the shuttle's rocket boosters could fail.

The memo was meant to jolt Morton Thiokol, the company that made the boosters and employed Boisjoly. The night before the Challenger's liftoff, the temperature dipped below freezing. Unprecedented for a shuttle launch, the cold prompted 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..

Boisjoly died in Nephi, Utah, near Provo, on Jan. 6. He was 73. His wife, Roberta, said he recently learned he had cancer in his colon, kidneys and liver.

Boisjoly was awarded the Prize for Scientific Freedom and Responsibility by the American Association for the Advancement of Science, and he spoke to universities and civic groups about corporate ethics. But before, he was cut off from space work and shunned.