Time-Horizon-Dependent Component Importance in a Solar-Powered Unmanned Aircraft System

Hardware reliability priorities may depend on the decision time scale, which a single importance ranking may obscure. A solar-powered unmanned aircraft system (UAS-A) for field-information support is assessed using a 21-event static fault tree, 17 minimal cut sets, an analytical solution, and Python (version 3.9.6) and MATLAB (R2025b) Monte Carlo implementations. The model targets hardware-induced loss of control under specified functional-loss criteria; software, human factors, weather and bird strikes remain outside its scope. With the compiled rate inputs and independent failures, the mean time to first failure (MTTF) is 43,038.8 h and the top-event probability at 24 h is 9.3701 × 10−5. Halving each component rate in turn gives a Spearman correlation of rS = 0.0546 between lifetime and finite-horizon sensitivity rankings throughout the sampled 1–48 h reference range. It rises to 0.939 at 8760 h and 0.996 near 40,000 h. First-order paths dominate short-horizon sensitivity under independence, while accumulated photovoltaic (PV) failures influence longer horizons. PV common-cause scenarios can elevate short-horizon PV priority. These horizons describe model evaluation; flight endurance requires an energy assessment. The workflow supports prioritization conditional on the functional topology, rate inputs and dependence model; emergency-return benefits additionally depend on detection and recovery sequences.