re: The Challenger exploded on this day 38 years ago...January 28, 1986.

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The cause of the disaster was the failure of the primary and secondary redundant O-ring seals in a joint in the shuttle's right 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. Shortly after liftoff, the seals were breached, and hot pressurized gas from within the SRB leaked through the joint and burned through the aft attachment strut connecting it to the external propellant tank (ET), then into the tank itself. The collapse of the ET's internal structures and the rotation of the SRB that followed threw the shuttle stack, traveling at a speed of Mach 1.92, into a direction which allowed aerodynamic forces to tear the orbiter apart. 

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