Advanced Coarse Sun Sensor (ACSS) is a device for sun-tracking and attitude determination. This sensor measures the incident angle of sun ray in two orthogonal axes, providing a high sensitivity based on the geometrical dimensions of the design. ACSS sun sensor offers the highest reliability and radiation hardness for the most demanding LEO, MEO and GEO missions. CSS technology of Solar MEMS has flight heritage since 2019 with hundreds of flight units delivered, and its manufacturing process has been developed and industrialized for mass production.