Gemini Summer by Iain Lawrence

Everyone in Danny River’s family has a passionate interest. Mom is writing a romantic novel in the basement. Dad is digging up the front lawn to build a bomb shelter. Danny’s brother Beau, determined to become an astronaut one day, is an enthusiastic fan of the Gemini space program. Danny’s own passion is dogs. He loves dogs, and they love him back! But his dream of having his own dog seems impossible.
Then tragedy strikes the River family, and everything changes. A dog does come into Danny’s life, but under circumstances that he never would have expected – or wanted. He names the dog Rocket. Who is this mysterious stray who limps into the Rivers’ yard? And how can Rocket and Danny help each other through the toughest year of Danny’s life?