Challenger broke apart 73 seconds after launch — a known O-ring flaw killed all seven crew

On the morning of January 28, 1986, the Space Shuttle Challenger launched from Cape Canaveral on a cold Florida day. Seventy-three seconds into the flight, it broke apart over the Atlantic, killing all seven crew members, including Christa McAuliffe, a schoolteacher set to be the first civilian in space. The disaster was watched live by millions, including schoolchildren across the United States.

The cause was the failure of rubber O-ring seals in a joint of the right solid rocket booster. The record-low temperatures that morning had stiffened the O-rings, so they could not seal the joint; hot gas leaked through, burned through the booster's attachment, and tore the shuttle apart. The danger was not new: test data going back to 1977 had shown the O-rings could erode and fail, but neither NASA nor the booster's manufacturer, Morton Thiokol, had fixed the known defect.

Most damning was the decision to launch at all. The night before, Morton Thiokol engineers had urged against launching in the cold, warning that the O-rings might fail. Under pressure from NASA managers eager to keep the flight on schedule, Thiokol's management overruled its own engineers and recommended the launch. The Rogers Commission, appointed by President Reagan, condemned NASA's organizational culture and decision-making, and physicist Richard Feynman demonstrated the O-ring's failure in ice water. The shuttle program was grounded for thirty-two months.