The City Among the Stars

Tankar Holroy, Lieutenant in the Stellar Guard of earth's Empire, floats in space after his spaceship is sabotaged. Rescued by an enormous, unknown ship, he awakes to discover himself saved by the People of the Stars who are born and live in space with minimal contact with planets and their occupants whom they call, with contempt, planetaries.
The chilly welcome he receives from the ship's leader, the Teknor, is followed by overt hostility from the other inhabitants of the Tilsin. Only a woman named Orena reaches out to him.
Tankar soon realizes that he was rescued for his knowledge of tracers, the technology that allows Empire ships to track others through hyperspace, a technology the People of the Stars lack. Out of spite, he refuses to deliver the one piece of knowledge that can protect the people who saved but now spurn him - and the consequences will be catastrophic.