C.S. Lewis’s trilogy beginning with Out of the Silent Planet is called the Space Trilogy.
The three novels follow Dr. Elwin Ransom through encounters involving other worlds, spiritual powers, scientific ambition, and moral conflict. The sequence consists of Out of the Silent Planet, Perelandra, and That Hideous Strength.
The first novel was published in 1938, followed by Perelandra in 1943 and That Hideous Strength in 1945. Although the books use science-fiction settings and concepts, Lewis also draws heavily on medieval cosmology, Christian theology, and debates about modern technology.
The trilogy is also known as the Ransom Trilogy or Cosmic Trilogy in some discussions, because Ransom is its central character and the stories span multiple worlds. “The Space Trilogy” is the standard English title for the group.