Tom Corbett, Space Cadet (1950)

Set during the middle of the 24th Century at the Space Academy (a training school for the Solar Guards) and aboard the 'Polaris', a Solar Guard training ship, this hugely-popular science-fiction series was one of the very few programs to air on all four major networks, including a brief period in 1951 when it ran on two networks simultaneously (NBC and ABC). It was seen three times weekly over CBS and ABC in fifteen-minute format, and in half-hour episodes on Saturdays over DuMont and NBC.