NASA’s The National Aeronautics and Space Administration (NASA) Challenger space shuttle, which had completed 9 successful Earth-orbiting missions, exploded just 73 seconds after lift-off in its 10th spaceflight. The tragedy marked NASA’s first-ever accident involving humans off-Earth, killing a 7-member crew. The mishap was blamed on faulty rubber O-rings which caused liquid oxygen and hydrogen fuel to mix, triggering an explosion.