The race to the moon dominated space flight during the the 1960s yet, during the late 1950s and early 1960s, the US Government sponsored a project that could possibly have sent 150 people on expeditions to Mars or Saturn. The project was code-named "Orion" and centred upon the effort to develop a fast, manoeuvrable, nuclear-powered space vehicle for long-range voyages in space. The proposed 4000-ton spaceship would be propelled by nuclear bombs but, strictly classified, the project was never given a chance to succeed or fail - due partly to its apparent absurdity - but its mix of sublime physics, madcap engineering, and a cast of Cold War warriors and would-be inter-galactic engineers made the mission a tantalising "what if" story. In this book George Dyson, son of physicist Freeman Dyson, one of the original project team, pieces together the story his father could only tell him in fragments at the time.