The eternal flame

"In an alien universe, the generation ship Peerless has set out to save its home world from annihilation. But the Peerless is facing urgent problems of its own. It does not carry fuel to return home, so without a new form of propulsion it will remain stranded in space.
A population explosion has stretched life support to its limits, and the biology of the travellers offers only one way to prevent growth: subjecting the women to famine to limit the number of children they bear.
When the astronomer Tamara discovers the Object - a massive meteor just within reach - hopes rise that there might finally be a solution to the fuel crisis. As an expedition is organised, a biologist struggles to devise a better way to control fertility, while his partner stumbles on a strange phenomenon that challenges everything she thought she knew.
As the three scientists clash with the prejudices of their society, they find themselves swept up in two dangerous revolutions: one in their understanding of matter and energy, the other in the roles imposed by their species on women and men. Either change may destroy the ship - together, they might save their world."