Poul Anderson 
Orbit Unlimited 

Earth had changed since the days when her proud space fleets spanned the void of Space. Now her people were packed and packaged tight on Earth, their freedoms exchanged for a promise of stability by a multi-armed autocratic government. Then one small band of people led by a fanatic saw there was one last chance for Man to make his place in the Universe. But to take that chance they had to fight, not only the mighty grip of the government, but the terrible, generation-long voyage fraught with risk. And then, the new planet – strange, challenging, alien…