Satellite propulsion systems are exposed to extreme environments, where high temperatures, intense pressures, and oxidative conditions push materials to their limits. To ensure structural reliability and performance across a wide range of missions, these systems require materials capable of withstanding such harsh conditions. Conventional superalloys and refractory metals have served well for decades, but their thermomechanical capabilities are now approaching saturation for modern propulsion demands. In this context, Refractory High-Entropy Alloys (RHEAs), composed of several principal elements in near-equiatomic proportions, have attracted significant attention. They offer exceptional strength, creep resistance, and thermal stability even at temperatures exceeding 1500 °C. This review explores the latest advancements in RHEA development and the growing understanding of their behavior from a multi-scale perspective, ranging from atomic-scale design to macroscopic performance under propulsion-like conditions. Particular focus is given to phase stability, oxidation resistance, and high-temperature mechanical properties relevant to satellite thruster environments. Furthermore, the role of computational alloy design, additive manufacturing, and data-driven optimization in accelerating RHEA innovation is discussed. The review concludes by identifying key challenges, such as intrinsic brittleness, high density, oxidation control, and material qualification, and outlines future directions for integrating RHEAs into next-generation spacecraft propulsion systems.