The Advanced Coarse Sun Sensor (ACSS) by Solar MEMS offers high reliability and radiation hardness for the most demanding LEO, MEO and GEO missions. The 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 technology has flight heritage since 2019 with hundreds of flight units delivered, and its manufacturing process has been developed and industrialized for mass production requested for satellite constellations. ACSS is a highly suitable sun sensor for satellite constellations and demanding missions due to its redundancy, reliability and hardness. Key features of the ACSS include: - 2 orthogonal axes - Analog, 15-pin micro connector electrical interface - Aluminum 6082, alodine + black anodizing housing - Manufacturing capacity of 100 ACSS per month - Each ACSS is calibrated, evaluated and tested - Quality control: > 50 inspection points/KC - EMC/ESD: ECSS-E-ST-20-07C, MIL-STD-461F - Reliability: 8 FIT @ 30 C - Flight heritage: > 500 years accumulated time in orbit without failures