Future space missions increasingly rely on habitable and pressurized modules that must offer flexibility, the possibility to extend their functionalities over time, and long operational lifetimes, often ensured through maintainability and in flight intervention. Standard satellite avionics are usually organized around centralized units such as the onboard computer, which concentrate processing, reconfiguration, and telemetry/telecommand handling in a single, tightly integrated design. Although this approach has a long heritage and provides dependable operation, it constrains how the avionics can be adapted to new mission profiles and makes late architectural changes disruptive and costly. Modular avionics address these limitations by distributing functionalities across a set of configurable, reusable building blocks, enabling system designers to assemble mission-specific configurations, introduce upgrades, and reuse elements across programs.