Space travel is tough.
No air, cosmic radiation, absolute lack of other life-sustaining essentials.
What better way to deal with space travel than to man ships with creatures that regenerate or don't need air, or are immune to various maladies? In a future world where zombies, vampires and werewolves co-exist with 'normal' humans on Earth, these ships are staffed by a motley crew of various types of undead or near-dead creatures.
Of course no one really knows what happens when zombies and vampires are squeezed together in the close confines of a spaceship.
Don't you love surprises?.