On January 28, 1986, the Space Shuttle Challenger was destroyed by an explosion 73 seconds after liftoff. All seven crew members were killed.
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The explosion happened because of the failure of a segment joint in the right SRB. When the joint failed, exhaust flames from the SRB cut into the External Tank like a blowtorch. The External Tank ruptured, its fuel ignited, and the tank exploded. The resulting turbulence destroyed the Orbiter.
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The joint failure was caused by a failure of the sealing system that protected the joint from the burning gases inside the SRB. Several factors combined to cause the failure of the sealing system. One key factor was that freezing temperatures on the morning of the launch caused the sealing system (or rubber "O-rings") to contract. This allowed the hot gases to burn through the sealing system and leak through the segment joint.
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Prior to the launch, engineers working on the SRBs were aware of problems with the segment joints. However, because of poor communication between the engineers and the launch managers, the launch went ahead anyway.
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The Space Shuttle program was suspended for more than two years after the Challenger accident. During that time, engineers fixed the problems in the original joint. And a presidential commission made recommendations to improve communication and decision making at NASA.
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The program resumed in September 1988 with the launch of Discovery.
