Lords of the Starship

The ship was to be seven miles long, a third of a mile in diameter and have a wing-spread of three and a half miles. It would take two and a half centuries to construct. Its announced purpose: to carry humanity away from its ruined world, from the world that had become a perpetual purgatory. To build this vast ship would require the undivided activity of an entire nation and would mean carrying out a ruthless program of war and conquest, of annihilation and reconstruction, and of education and rediscovery.
But was this starship really what it was claimed to be? Or was there a greater secret behind its incredible cost - a secret so strange that no man dared reveal it?