This thesis focuses on the design and development of a modular Remote Terminal Unit (RTU) for small satellite platforms operating in Low Earth Orbit (LEO). The RTU serves as a central interface between the On-Board Computer (OBC) and the satellite's Attitude and Orbit Control System (AOCS), managing power distribution, telemetry acquisition, and actuator control in a compact and highly integrated avionics module. The proposed RTU is designed to interface with a wide range of AOCS equipment, including star trackers, sun sensors, magnetometers, gyroscopes, GNSS receivers, magnetic torquers, reaction wheels and reaction control systems. To achieve this, it integrates both analog and digital signal acquisition capabilities and supports multiple communication standards.