The moment Lieutenant Alison Ash steps aboard the Persephone, she knows her life will never be the same. She will never again watch the sun rise over the asteroid belt, never again see Earth from a handheld telescope, and never again see her family.

In less than three weeks, the ship will dock at the Posterus and begin the most important journey humankind has ever undertaken. More important than discovering fire, creating language, or even abandoning Earth to live confined in biospheres among the asteroid belt over 100 years ago.

What Ash doesn't expect is that by keeping her recent...