C.S. Lewis’s trilogy beginning with Out of the Silent Planet is called The Space Trilogy.
The trilogy follows the philologist Elwin Ransom through encounters involving other worlds, scientific ambition, and spiritual conflict. Out of the Silent Planet appeared in 1938, followed by Perelandra in 1943 and That Hideous Strength in 1945. The books combine planetary adventure with Lewis’s interest in medieval cosmology, Christian theology, and the moral dangers of treating science as an unlimited power.
The books are also known collectively as the Ransom Trilogy, after their protagonist. “Space Trilogy” is the standard title used for the group, while “Cosmic Trilogy” is an occasional descriptive label rather than the usual canonical name. Unlike The Chronicles of Narnia, the trilogy is aimed primarily at adult readers and is set in a more recognizably modern world, even when its action extends beyond Earth.