Space Shuttle Challenger Explosion
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NASA's space shuttle Challenger completed 10 missions before it broke apart during a launch in 1986, killing seven astronauts.
Former astronaut and professor Terry Hart is opening up 40 years later about the friends and colleagues he lost on board the space shuttle Challenger explosion.
TODAY marks four decades since the Challenger space shuttle exploded just 73 seconds into its flight. Millions watched the disaster unfold live, as the tragedy was broadcast in schools and on TV