The swashbuckling science-fiction hero, Buck Rogers style, can be a pretty depressing fellow. In "Lucky Starr and the Rings of Saturn" … Paul French tells us how Lucky spoils the Sirians' plans to colonize one of our sun's planets. Studded with what one supposes are spaceman epithets, such as "Great Galaxy!" and "Sands of Mars!", this is a good guy vs. bad guy situation in which neat plotting is the saving grace of an otherwise ordinary effort.