"The Has-Been Superman!"
While trying to close an inter-dimensional gap in space above the Earth, created by a U.S. military expeirmental bomb, Superman is exposed to a liquid that causes him to permanently lose his powers. Too proud to stop being a hero, he adopts the identity of Nova and uses Kryptonian devices to start a new career. This story concludes in World's Finest Comics #180.
Note: The Nova that appears in this story is not related to the Marvel Comics character.
"Rip Van Superman" reprinted from Superman (1939) #107.