The Sun Runners

Lieutenant Adeheid Koning was only twenty-three when the Earth's long fight against its environment ended in collapse and nuclear war. Earth's sudden silence leaves the colonies of the inner solar system without life-lines, in various stages of self-sufficiency. Or, in Mercury's case, not. To help her fellow stranded colonists of Mercury survive against starvation and a breakdown of order, Adelheid fights against some cold equations and makes some hard choices, ending up wearing an iron crown as queen of one of the rail cities of Mercury, constantly moving to stay ahead of the Sun.
Fifty years later, Adelheid's granddaughter Frieda is a seventeen-year-old princess who would rather be an engineer. Frieda's life is shattered when a suspicious accident takes one of her arms--and is then turned upside-down when her mother dies from that accident. Frieda is left a young and vulnerable queen, locking horns with her grandmother, who is now regent and dowager.
When the Earth makes contact again, after fifty years of silence, Frieda is eager to end Mercury's isolation, but Adelheid is suspicious of the Earth's sudden return, and wary of the other latitude towns' desires to accept all that the Earth is offering, without question.
With thousands of lives on the line, is it wise to hope for healing? Or are we forever defined by what we do in the dark?