This paper explores the synergistic integration of microprocessor-based intelligent cyber defence mechanisms with high-speed data encryption techniques for Low Earth Orbit (LEO) spacecraft. As LEO constellations become critical infrastructure, ensuring their cybersecurity and the confidentiality of transmitted data is paramount. We investigate novel microprocessor architectures and intelligent algorithms for real-time threat detection, intrusion prevention, and autonomous response tailored to the resource-constrained environment of LEO satellites. Furthermore, we delve into advanced cryptographic methods optimized for high-throughput data streams and the unique challenges of space-based communication, including latency and intermittent connectivity. The paper proposes a layered security framework that leverages on-board intelligent processing for proactive cyber defence and robust encryption to safeguard sensitive data transmitted to and from LEO assets. The potential benefits of this integrated approach include enhanced resilience against cyber threats, improved data security, and increased operational efficiency for future LEO missions.