Optical Communication Terminals (OCTs) integrate photonic and electronic technologies to enable high-speed, secure, and interference-free space communication. Deployment across multiple orbital regimes exposes these heterogeneous systems to diverse radiation environments, each presenting distinct failure mechanisms that challenge conventional Radiation Hardness Assurance (RHA) approaches, particularly for cost-constrained Small Satellite (SmallSat)-class missions where economic feasibility must be balanced against radiation hardness requirements. This paper presents a multi-orbit radiation effects investigation for photonic-electronic architectures by characterizing environment-specific vulnerabilities and failure modes across Sun-Synchronous Orbit (SSO), Low Earth Orbit (LEO), and Middle Earth Orbit (MEO). SPENVISbased environment analysis shows that SSO presents a mild radiation environment with Total Ionizing Dose (TID) below 1 krad(Silicon (Si)) per year at 4 mm Aluminium (Al) shielding and low charged particle flux. LEO is dominated by proton-induced Single Event Effects (SEEs) with moderate TID, and MEO exhibits TID exceeding 30 krad(Si) per year at the same shielding level, together with relatively higher heavy-ion fluxes that drive SEE rates. Technology-level analysis reveals fundamental differences between photonic and electronic subsystems. Photonics exhibits predominantly parametric degradation that can be mitigated through margin allocation, whereas electronics remains susceptible to discrete, stochastic failure modes requiring active mitigation. These findings motivate reconfigurable architectures leveraging Field Programmable Gate Arrays (FPGAs), radiation-tolerant photonic subsystems,Wide-Bandgap (WBG) power semiconductors, and emerging Non-Volatile Memories (NVMs) to enable component-level commonality across orbital regimes. Additionally, photonic devices require parametric end-of-life characterization with explicit translation to link budget margins, while electronic systems require mission-tailored mitigation strategies and system-level testing.

In this paper, a comprehensive review of the evolving engineering and testing methodologies for radiation hardness assurance (RHA) in commercial-off-the-shelf (COTS) based space avionics, with a focus on recent trends and future directions is provided. The increasing reliance of space engineering on COTS has prompted a shift in RHA strategies, reflecting both technological advances and the complex radiation environments faced by modern space systems. Emphasis is placed on the interplay between traditional RHA frameworks and the integration of state-of-the-art design principles, fault-tolerant architectures and testing approaches. The review highlights how evolving system requirements and accelerated development cycles have influenced radiation testing practices and risk mitigation techniques. Examples are presented of enhancing reliability under radiation exposure, including reconfigurable systems, agile engineering processes and system-level validation. Emerging applications, including intelligent onboard systems and distributed satellite networks, are discussed with attention to their unique challenges and opportunities in RHA. The review concludes with a perspective on the critical gaps and future needs to advance RHA practices in support of increasingly complex and resource-constrained space missions.