Study on a Retrofit-Friendly Solid-State Circuit for Legacy Electromechanical Relay Applications

Electromechanical relays have long been employed in aerospace and defense platforms, including spacecraft, missiles, and aircraft, for power control, discrete switching, and pyrotechnic initiation. However, their mechanical construction makes them vulnerable not only to vibration and shock but also to contact wear and degradation, raising concerns about long-term reliability in flight environments. This paper introduces a retrofit-friendly solid-state circuit that replaces conventional relays while preserving backward compatibility. Notably, the proposed retrofit design considers a hybrid configuration of electromechanical and electronic elements, enabling mixed deployments without system-level redesign. Experimental validation, including high temperature exposure and interoperability tests, demonstrates that the circuit maintains functional equivalence to electromechanical relays while offering improved robustness. These results indicate that the retrofit approach provides a practical pathway to enhance reliability and maintainability in mission-critical aerospace systems, bridging the gap between existing architectures and modern solid-state technology