Downbelow Station.

From back cover Daw paperback February 1981:

Pell's Star occupied the central spot in the coming conflict between Earth's tired stellar empire and the tough onslaught of its rebellious colonies. Whoever controlled Pell's Downbelow station held the key to Earth's defensive perimeter -- or the jumping off point for a Terrestrial offensive to regain the lost empire.

But Pell had always been neutral and was determined to remain so.

This is a powerful, complex, and enthralling novel of interstellar conflict and ambitions. In its pages you will meet and strive with many vivid persons, human and non-human, who futures would hang on the outcome of that titanic struggle.