In May 2018 NASA called a press conference to announce the successful test-run of their tiny nuclear reactor KRUSTY (Kilopower Reactor Using Stirling Technology). This revolutionary technology, which runs on heat alone, may have profound consequences for the future of mankind, enabling us to maintain permanent bases on the Moon, on Mars, and other planets, and eventually power a starship. On earth too it could have enormous benefits as a new way to generate power at a time when climate change is threatening our very existence.This book is the amazing story behind this invention, which began with Robert Stirling's original designs for a heat exchange engine in 1816. An invention truly ahead of its time, the practical application of the Stirling Engine has taxed the minds of scientists and inventors for almost 200 years. Only now is it possible for its full potential to be realized. Phillip Hills weaves science and history together to tell the story of one of the most exciting scientific developments the world has ever seen.