Progressive Radiation Hardness Assurance for COTS SmallSat Avionics Beyond LEO

As SmallSat missions extend beyond Low Earth Orbit (LEO), traditional Radiation Hardness Assurance (RHA) approaches based on linear qualification workflows are increasingly mismatched with Commercial-Off-The-Shelf (COTS)-based avionics programmes. This paper presents a progressive RHA methodology applied to photonic and electronic avionics that treats radiation assurance as an iterative design activity. The methodology is grounded in a fundamental asymmetry between the two domains. Photonic subsystems exhibit parametric degradation, while electronic subsystems are susceptible to stochastic failure modes. This asymmetry motivates a multi-pathway Hardware-in-the-Loop (HiL) fault injection platform built around a Zynq UltraScale+ Multi Processor System-on-Chip (MPSoC) modem for Optical Communication Terminal (OCT) applications. The platform combines a variety of fault injection methods, enabling independent and combined assessment of fault mechanisms across the full signal chain. The progressive approach shifts risk identification earlier in the design cycle, reducing reliance on costly late-stage qualification and enabling more efficient allocation of beam facility resources.