Space Shuttle Challenger Explosion
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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.
On Jan. 28, 1986, the Space Shuttle Challenger exploded 73 seconds after takeoff. All seven crewmembers on board were killed.
Wednesday marks a somber anniversary in American history. 40 years ago, seven astronauts were killed when Space Shuttle Challenger exploded during liftoff.