<p>Effective thermal control is essential to ensure the operational integrity of Cu-beSat subsystems exposed to harsh thermal fluctuations in low earth orbit (LEO). This study investigates the influence of the β-angle, defined as the tilt between the orbital plane and the solar vector, on the thermal behavior of a 1U CubeSat. A high-fidelity thermal model was developed using COMSOL Multiphysics to simulate transient temperature distributions. To reduce computational cost, a regression-based surrogate model was constructed for fast and accurate thermal predictions. Probabilistic reliability analysis was conducted using importance sampling, subset simulation, and Monte Carlo methods to assess thermal failure risks under extreme orbital conditions. Finally, a multi-objective optimization strategy employing simulated annealing, particle swarm optimization, differential evolution, and Nelder-Mead algorithms was implemented to identify the optimal β-angle. The proposed methodology integrates modeling, reliability, and optimization into a unified framework, offering a novel and efficient approach to improving CubeSat thermal management and supporting space mission design.</p>