I would like to suggest an interesting book and a very good read on the early unmanned spaceflight programs right up to the Voyagers.
Rewind to the 1950s and ponder: was America’s first satellite really built by a college student? How did a small band of underappreciated Russian engineers get pictures of the moon’s far side—using stolen American film? As the 1960s progressed, consider: how the heck did people learn to steer a spacecraft using nothing but gravity? And just how were humans able to goose a spaceship through a thirty-year journey to the literal edge of our solar system?
To buy or read more about this book visit http://www.nebraskapress.unl.edu/product/Ambassadors-from-Earth,674133.aspx