An American author of both science fiction and non-fiction, he is particularly known for his Grand Tour series. His other works include Maxwell's Demons (1979) and Exiled from Earth (1971).
After graduating from Temple University, he worked as a technical writer for Project Vanguard.
For his work as an editor at Analog Science Fiction, he received six Hugo Awards.
He married Rosa Cucinotta in 1953. The couple had two children before divorcing in 1974.
He was a recipient of the Hugo Award, an honor named after author Victor Hugo.