The Burning Bridge by Poul Anderson, Science Fiction, Adventure, Fantasy

The fleet numbered fifteen, more than half the interstellar ships humankind possessed. But Earth's overlords had been as anxious to get rid of the Constitutionalists (the most stubborn ones, at least; the stay-at-homes were ipso facto less likely to be troublesome) as that science-minded, liberty-minded group of archaists were to escape being forcibly absorbed by modern society. Rustum, e Eridani II, was six parsecs away, forty-one years of travel, and barely habitable: but the only possible world yet discovered. A successful colony would be prestigious, and could do no harm; its failure would dispose of a thorn in the official ribs. Tying up fifteen ships for eight decades was all right too. Exploration was a dwindling activity, which interested fewer men each generation.