Titan (1979)

A scientific expedition to the planet Saturn in 2025, aboard the ship Ringmaster, discovers a strange satellite in orbit around the planet. Commanding the ship is Cirocco Jones, a tall NASA career woman, aided by astronomer Gaby Plauget, the clone twin physicists April and August Polo, pilot Eugene Springfield, physician Calvin Greene and engineer Bill (whose last name is never given).

As they reach the satellite they realize it is a huge hollow torus, a Stanford torus habitat. Before they can report this, the ship is entangled in cables from the object. The crew is rendered unconscious and later wake up inside the habitat. Initially separated, Cirroco and Gaby find each other and travel together through the world inside the torus to find the rest of the crew.