Challenger, U.S. space shuttle. It exploded (Jan. 28, 1986) 73 seconds into its tenth flight, killing all seven crew members, including the first civilian in space, schoolteacher Christa McAuliffe. The disaster was caused by the faulty design of a gasket (the O-ring seal). As dramatically demonstrated by Richard Feynman, a member of the presidential commission appointed to investigate the accident, the elastic O-ring did not respond as expected because of the cold temperature (30°F/-1°C) at launch time. (At a news conference, Feynman illustrated the loss of elasticity by dropping an O-ring into a glass of cold water.) As a result of the explosion, the United States did not send astronauts into space for almost three years as the National Aeronautics and Space Administration redesigned a number of features of the space shuttle.