From the introduction:
Cat Astronauts on Mars is a game to be played with a child while out on a walk. In the game, you pretend that you are cat astronauts having adventures, and that the neighborhood around you is actually Mars. I.e., “that field in front of the school is actually a wide open dusty plain, and the school is giant mountain range”.
Of course, we know that this doesn’t make any sense. But half of the fun of playing with children is watching them transform the everyday mundane world around you into the magical and fantastical. Plus, if you have a child that loves space and cats, they will be all too happy to play this game.