Complex sentence: The Bussard ramjet is a theoretical method of spacecraft propulsion proposed in 1960 by the physicist Robert W. Bussard, popularized by Larry Niven in his Known Space series of books, and referenced by Carl Sagan in the television series and book'.
Split into simpler sentences: The Bussard ramjet method of spacecraft propulsion was proposed in 1960 by the physicist Robert W. Bussard. It was popularized by Larry Niven in his Known Space series of books and referenced by Carl Sagan in the television series and book'.