Seventy-three seconds

Challenger broke apart on the coldest morning any shuttle had ever launched in, after a rubber seal that had never been tested that cold failed to close a joint.

Engineers at the booster contractor had argued against launching the night before and been overruled. Richard Feynman's demonstration at the hearing — a piece of the O-ring, a glass of iced water, a C-clamp — did more to explain it to the public than the rest of the report combined.