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This is a story about a family of "Loonies" (i.e., Lunar citizens with a sense of humor) who buy a used spaceship and go sightseeing around the solar system. The twin teenaged boys, Castor and Pollux, buy used bicycles and hope to sell their cargo at a profit. Their sister sings on their radio show in the asteroids. Their kid brother Buster has the highest IQ of the whole family, and no one but granny Hazel can keep him in line. A Martian flat cat named Fuzzy Britches, born pregnant and producing a soothing vibration (compare tribbles), makes more trouble and more money than anyone thought possible. Then Buster and Hazel get lost in the Asteroid Belt, and Hazel almost dies before they are rescued by the twins.
A condensed version of the novel had been published earlier in Boy's Life under the title "Tramp Space Ship."
The British rock group The Rolling Stones did not take their name from Heinlein's book. They named themselves after a Muddy Waters song, after at least two other bands had considered and then discarded the name.