The Ships of Earth by Orson Scott Card -- 351 pages
The City of Basilica has fallen. Now Wetchik, Nafai, and all their family must brave the desert wastes, and cross the wide continents to where Harmony's hidden spaceport lies silent, abandoned, waiting for the command to make the great interstellar ships ready for flight again.
But of these sixteen people, only a few have chosen their exile. The others, Rasa's spiteful daughters and their husbands; Wetchik's oldest son, Elemak, have been forced against their will. Their anger and hatreds will make the difficult journey harder.
This is book 3 of the Homecoming series.