Heaven Chronicles — Joan D. Vinge

Heaven System has no habitable planets, but Heaven Belt asteroids once supported space colonies richer and more advanced than even Earth...

Until the Civil War. Now Heaven Belt is a vast ruin, where the yet-living prey on the artifacts of the dead. Where pockets of humanity use failing machines and radiation-leaking ships to battle over fragments of lost science in the fading hope of surviving another generation, another year.

Meanwhile, light-years away, Morningside Colony desperately gambles scarce resources, building a single ship to seek the Belt's help. Seven brave men and women are now flying toward Heaven...

And have just crossed the border into Hell.