The Cosine Sun Sensor (CoSS) delivers coarse information about the position of the sun relative to the spacecraft. This information is used for coarse maneuvering of the spacecraft and to inform the spacecraft about the position of the sun.
The CoSS delivers coarse information about the polar angle of the sun. This information is derived from the fact that the sensor output varies approximately proportional to the Cosine function of the angle of incidence of sunlight.
With a suite of CoSS, of which at least three sensors with different viewing directions have the sun in their field of view, the Attitude & Orbit Control Subsystem (AOCS) can retrieve the position of the sun in the coordinate reference system of the spacecraft. Typically there are eight to twelve CoSS per space platform.