Space Shuttle Challenger explosion on January 28th, 1986

On January 28th, 1986, the Challenger shuttle (STS-51) exploded 73 seconds after lift-off.
A pressure seal in the aft field joint of the right Solid Rocket Booster failed during the shuttle blast off. This created a hot gases leak that rapidly turned into a flame, pulling away the lower strut linking the Booster and the External Tank, permitting the Booster to rotate around the upper attachment strut and making it collided with the external tank filled with 600 tonnes of liquid hydrogen and oxygen. This resulted into the shuttle explosion.
The accident was fatal for the seven astronauts. The NASA does not know whether they were alive and conscious during the cabin fall (which lasted 2 minutes and 45 seconds).