Tin-based perovskites are among the most promising candidates for high performance light-weight and radiation-tolerant space photovoltaics, but their response to energetic proton fluxes is not adequately determined. In this work, integrated SCAPS–SRIM analysis was applied to lead-free MASnI₃ perovskite solar cells for space applications in order to correlate device optimization with proton-radiation response. We established a combined SCAPS–SRIM simulation platform to simulate optoelectronic behaviors and radiation tolerance of an Au/Cu₂O/MASnI₃/TiO₂/FTO solar cell under AM0 illumination. Optimal-device calculations demonstrate that device absorber thickness of 0.20–0.30 µm and a TiO₂ ETL of 20–50 nm, Cu₂O HTL of 50 nm thicknesses result in good carrier collection and minimized recombination losses. Quantum efficiency and J–V measurement illustrate a stable operation under AM0 light, verifying the no extrinsic spectral incompatibility of MASnI₃ for the space energy source application. SRIM proton irradiation simulations (10-250 keV, 0° incidence) highlight the most damaging energy range within 50–150 keV for which masked Bragg peak lies in proximity to the MASnI₃ absorber and MASnI₃/TiO₂ interface accompanied by enhanced vacancy density, recoil energy deposition and phonon generation. High-energy protons (>200 keV) which deposit most of their damage in the rear contact stack, minimizing absorber degradation. The results overall indicate that MASnI₃ holds a good optoelectronic performance beyond the predictable radiation-damage behavior and thus can be considered as a promising alternative for space photovoltaic technology