This Day in History:, Challenger Disaster.br January 28, 1986.br 73 seconds after its 11:38 a.m. launch, br NASA's space shuttle exploded, br killing all seven crew members.br Among the crew was Christa McAuliffe, br a 37-year-old high school social br studies teacher from New Hampshire.br McAuliffe had won a br competition that earned br her a place on the Challenger.br Millions witnessed br the tragedy on live television.br In the aftermath, President Ronald Reagan br appointed a special commission to br determine what went wrong with Challenger.br The investigation determined br the disaster was caused by br the failure of an “O-ring” seal br due to cold weather.