The Gemini space flight program is all but forgotten, having been eclipsed by the spectacular drama and success of the Apollo flights to the Moon. Neither was it a pioneer, coming after the heroic and pathfinding Mercury project. But whereas Mercury was derided as 'spam-in-a-can' and Apollo was a truck towing a lunar lander, the Gemini spacecraft was an agile flying machine for fighter pilots. Initially called the Mercury Mark II, it gave the United States the tool it needed to learn how to fly in space, and in so doing it prepared the country's space agency, NASA, to set off for the...