Comparative Investigation of Radiation-Driven Failure Mechanisms in Photonic-Electronic Optical Communication Terminals Across Earth Orbits

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.