Seeds: The Journey Begins — Cary Allen Stone

Conditions on Earth are both dangerous and dire. The leaders of nuclear-armed countries are on high alert, prepared for war. The Strategic Extra-Earth Development Site has spent years preparing a ship to leave for Titan, one of Saturn's moons. The unhinged President orders the launch of all warheads. The subsequent nuclear holocaust kills all living things on Earth. The ship is able to depart with the last of humanity to build a new world.