"Tortoise and Hare", a novella by Kevin J Anderson, tells the story of Jorie Taylor, who has lived her whole life on the generation ship Beacon. Fleeing an Earth tearing itself apart from its exhaustive demand for resources, the Beacon is finally approaching Sarbras, the planet circling Tau Ceti which they hope to make humanity's new home.
But Earth has recovered from its near-death experience, and is now under the control of a ruthless dictator whose sights are set on Tau Ceti as well. President Jurudu knows how to get what he wants - and he wants Sarbras. He sends the military ship Conquistador, which uses newly-developed FTL (faster-than-light) technology, to ensure that he gets it.
In the sequel novelette "Grasshopper and Ants" by Steven Savile, Jorie is now the eleventh captain of the generation ship Beacon, which has at last reached its destination, the colony planet Sarbras. But one by one, the colonists come down with a mysterious, undiagnosible illness. And the Conquistador's arrival is imminent.
Tau Ceti won the 2013 "Lifeboat to the Stars" Award as the best work of science fiction contributing to an understanding of the benefits, means, and difficulties of interstellar travel.