Technicians discovered a stripped bolt on the exterior hatch handle of the Space Shuttle Challenger, forcing a launch delay from January 27 to the next morning. Overnight temperatures plunged into the low 20s Fahrenheit, conditions that engineer Roger Boisjoly and others at Morton Thiokol had specifically warned could cause O-ring seals to fail. The launch proceeded the next day anyway, ending in the disaster that killed all seven crew members 73 seconds after liftoff.
The scrub on January 27 was almost farcical in its mundanity: a ground crew member's attempt to remove the hatch's exterior handle stripped a bolt, and by the time a new bolt was sourced and drilled out, high winds had picked up at the shuttle landing strip, ruling out a safe abort-to-launch-site scenario. NASA pushed the launch to the following morning.
That delay proved consequential. Overnight temperatures at Kennedy Space Center dropped to around 24°F, far colder than any previous shuttle launch. Engineers at Morton Thiokol, which manufactured the solid rocket boosters, held an anguished conference call that evening; Roger Boisjoly and Allan McDonald argued forcefully that the rubber O-rings sealing the booster joints had never been tested below 53°F and could stiffen and fail to seal properly in the cold. Thiokol managers, under pressure from NASA officials eager to avoid another delay, overruled their own engineers and approved the launch.
The next morning, January 28, Challenger lifted off in freezing conditions with icicles still visible on the launch tower. A failed O-ring seal allowed hot gas to escape, igniting the external fuel tank 73 seconds later and destroying the vehicle, killing all seven aboard including teacher Christa McAuliffe. The scrubbed day before is now remembered as the last, missed chance to avert the catastrophe.
Key people: Roger Boisjoly, Allan McDonald