On January 28, 1986, the Space Shuttle Challenger exploded 73 seconds into its mission off the shore of Cape Canaveral. The spacecraft made it 46,000 feet into the air, exploded at approximately 11:39 A.M. The explosion marked the first fatal accident involving an American spacecraft while in flight. The explosion was discovered to have been caused by a shrunken O-ring on the spacecraft, which shrunk due to cold weather. The O-ring seals a joint in a shuttle's solid rocket booster. The crew’s mission was intended to orbit the Earth and deploy a communications satellite to study Halley’s Comet. All 7 crew members were killed instantly upon the explosion. The most notable was Christa McAuliffe, who was a school teacher picked for the job by President Ronald Reagan’s Teacher in Space Project. Unfortunately, many young students in classrooms had watched this horrible tragedy, and many people still remember that day.