From Halopedia, the Halo wiki
Coordination platforms (also known as defense platforms and sensor battlements) are a type of space station formerly employed by the Covenant empire, prior to its collapse. Coordination platforms were managed by the Ministry of Concert and placed in every star system inhabited by the empire, allowing the ministry to monitor the system's population, support tithe-ships and monitor heretics. While often used to stock a ministerial garrison for military functions, they also served important civil and religious functions - serving as outposts for the Covenant's ecclesiarchy and as nodes in the empire's proselytization network for communications.
In war, the Covenant's military generally employed smaller forms of these outposts for similar purposes in locations of strategic interest such as mining sites, fuel processing stations and repair centers.
- Halo Encyclopedia (2022 edition), page 225