1969 – NBC-TV canceled “Star Trek.” The show had debuted on September 8, 1966.

Sept81966: Liftoff for the Starship. 1966Star Trek makes its network television debut. Given the cultural impact and enormous franchise spawned by the originalStar Trek series, it’s hard to believe that the show lasted just three seasons – 80 episodes – and was canceled by NBC in 1969 because of low ratings.

resource: wired.com