The Rolling Stones

The Stone family, lunar-born, technically minded, and perpetually restless, buy a secondhand spaceship and set off from the Moon on a family tour of the solar system. Teenage twins Castor and Pollux have their own side hustle in mind, planning to buy up used bicycles on Mars and resell them at a markup, but a small furry souvenir picked up along the way, a Martian 'flat cat' bought for their little brother, turns out to have habits that could sink the whole trip's finances. Robert A. Heinlein's family adventure blends hard-edged space travel with comic domestic chaos.