Space boy and his dog

"Niko may live on boring old Earth with his family, but he's always finding a new adventure. Using the spaceship that he built from a box in his backyard and a little imagination, he flies off into space with his robot Radar and his dog Tag. The only one NOT invited is his sister Posh, who keeps trying to insert herself into Niko's story. In this first mission, Niko and crew (and maybe also pesky Posh) fly to the moon in search of a lost cat"--Amazon.com.