The cause of the disaster was the failure of the primary and secondary O-ring seals in a joint in the right Space Shuttle Solid Rocket Booster (SRB). The record-low temperatures on the morning of the launch had stiffened the rubber O-rings, reducing their ability to seal the joints. (STS-51-L crew: (back) Onizuka, McAuliffe, Jarvis, Resnik; (front) Smith, Scobee, McNair, NASA Image)