- "Tidens frø" (1956)
- "The Space-Born" (1959)
- "Sargasso of Space" (1961)
- "Manden i månen" (1963)
- "Manden i himlen" (1966)
- "Stenen fra Saturn" (1968)
- "Den tavse invasion" (1969)
- "Krystalpaladset" (1971)
- "Tidsstormen" (1973)
- "The Tower of Glass" (1975)
- "The Star-Sent" (1977)
- "The Secret of the Red Lily" (1978)
- "The Circle of Fire" (1979)
- "The Web of Time" (1980)
- "The Ring of Ice" (1981)
- "Nøglen til uendeligheden" (1982)
- "The Dark Nebula" (1983)
- "Det kosmiske øje" (1984)
- "The Final Key" (1985)
Faglitteratur:
- "Strontium 90:The Fate of Man" (1958)
- "The Outer Space Handbook" (1959)
- "The Race for Space" (1961)
- "Udforskningen af rummet" (1963)
- "Astronomi for begyndere" (1964)
- "The Planets of Our Solar System" (1966)
- "The Universe:A Guide to the Mysterious Cosmos" (1968)
- "The New Handbook of Space" (1971)
- "The Conquest of Space" (1973)
- "Life Beyond Earth" (1975)
- "Cosmic Journeys:A Pictorial Tour of the Universe" (1977)
- "The Black Hole:A Guide to the Darkest Mystery in Space" (1978)
- "The Edge of Space" (1980)
- "The Ultimate Frontier:A Retrospective of Space Exploration" (1982)
- "Vores plads i universet" (1984)
- "The Last Frontier:Beyond the Solar System" (1986)
- "The Frontiers of Astronomy:A Guide to the Expanding Universe" (1988)