Cosmos 661

Cosmos 661 is a satellite of the Tselina-OM constellation. Tselina-OM is a Russian, formerly Soviet, military space-based radio surveillance system. It is capable of determining the exact location of radio-emitting objects and also their type, modes of operation, and how active they are. For instance, preparation for a military operation may raise the activity of the radio communications. Detection of these communications by a space-based surveillance system can provide early warning of this activity, warning that may be unavailable by other means.