Autonomy and adaptivity are becoming architectural necessities in modern satellite missions, where communication delays, environmental uncertainty, and limited ground intervention require onboard reasoning capabilities. However, integrating runtime self-adaptation within safety-critical space systems remains challenging due to strict certification, partitioning, and assurance constraints. This Journal-First paper summarizes our recently published work proposing a Reference Architecture for autonomous and adaptive satellite systems. The architecture is derived from a Systematic Literature Review of 29 studies and structured through a Design Science Methodology. It integrates the MAPE-K feedback loop with ECSS-aligned software partitioning, reconciling adaptive reasoning with safety-driven architectural decomposition. The architecture is validated through expert assessment and instantiated on the NIMBUS satellite platform developed by Thales Alenia Space Italy (TAS-I), demonstrating its feasibility in an industrial and safety-regulated environment.