STS-51-L (Challenger)

On January 28, 1986, the Space Shuttle Challenger broke apart 73 seconds after liftoff, killing all seven crew members, including teacher Christa McAuliffe, who was to have taught lessons from orbit to millions of schoolchildren. A rubber O-ring seal in the right solid rocket booster, stiffened by the morning’s freezing temperatures, failed and let hot gas burn through to the external fuel tank.

The Rogers Commission investigation — with physicist Richard Feynman’s famous ice-water O-ring demonstration — exposed not just a hardware flaw but an organizational one: schedule pressure and normalized risk had overridden engineers’ warnings. The disaster grounded the shuttle fleet for 32 months and reshaped NASA’s safety culture, a legacy invoked in every human spaceflight program since.