Horizon Sensor for Nano and Micro Satellites (HSNS) of Solar MEMS is a Quad Thermopile sensor for Earth detection and Nadir vector determination. This device measures the infrared radiation from Space and from Earth with 4 IR-eyes, providing accurate and reliable detection and attitude determination. HSNS is based on previous experience of Solar MEMS making attitude sensors and long research projects on IR sensing devices. Every HSNS is characterized and tested, and includes a microcontroller for fast assembly and integration with different options like UART or I2C protocols.