In recent years, the satellite industry has evolved significantly. The emergence of the so-called new space has been a real disruption in the space sector. This field was born thanks to the appearance of nanosatellites, small, lower-cost satellites with faster development times. It is an area with a strong commercial focus in the creation of its solutions and services. The software design of satellite systems has improved substantially with the adoption of Integrated Modular Avionics (IMA)-based architectures that have been the main drivers of significant reduction in weight, size and power. This technology has played a key role in this transformation, enabling satellites to perform complex tasks with greater efficiency. The IMA-for Space (IMA-SP) based design facilitates the use of a common execution platform to run applications with different levels of criticality. This paper presents a comprehensive overview of cybersecurity concerns in partitioned architectures for satellites, highlighting key elements such as partition isolation, secure communication, memory management, and scheduling. The unique characteristics of the space environment and the “new space” paradigm introduce specific security challenges that demand tailored approaches. The threat landscape for these systems is analysed, and a security architecture based on dedicated partitions is presented and proposed. Additionally, implementation challenges, security-performance trade-offs, and future research directions in light of emerging threats are examined.