Impact of GCR and SPE on space radiation shielding: OLTARIS simulation and quantum optimization of material selection using quantum algorithms

During long-term deep-space missions, a key challenge to the human and spacecraft is the space radiation, which is coming from the three different sources: Galactic Cosmic Rays (GCRs), Solar Particle Events (SPEs), and trapped particles in regions of Van Allen belts. High-energy particle radiation can have harmful effects on the spacecraft systems, sensors, electronic components, and astronauts, compromising mission reliability. This makes effective shielding a critical requirement. Traditionally, passive shielding materials such as aluminum have been used, but their limitations, especially in generating secondary radiations, necessitate the search for more efficient alternatives. In this study, the performance of various shielding materials, such as Lithium hydride (LiH), Polyethylene (C₂H₄), Lithium borohydride (LiBH₄), Beryllium borohydride (Be(BH₄)₂), and Ammonia borane (NH₃BH₃) is systematically evaluated in the GCR and SPE environment using On-Line Tool for the Assessment of Radiation in Space (OLTARIS), a NASA (National Aeronautics and Space Administration)-developed simulation tool. Further, the effect of SPEs (October 1989) on the performance of shielding materials is studied and evaluated through particle flux distributions (energy spectrum) and equivalent dose distributions for these materials. The relative shielding effectiveness of these materials in the SPE environment varied from that in the GCR environment, suggesting that material performance is dependent on the radiation environment. Beryllium borohydride (Be(BH₄)₂) emerges as the best material in the SPE environment, while lithium hydride (LiH) gives the least dose equivalent in the GCR environment. The particle-wise dose equivalent and flux contributions reveal that, in the SPE environment, the material performance is directly linked to the hydrogen content of the material. In addition, the effect of solar modulation on dose equivalent in the GCR environment is studied. As solar modulation increases, the GCR intensity reduces and hence dose equivalent also reduces. As the space radiation environment consists of complex particle radiation of high energies, in order to validate the large sample of materials for space radiation shielding, the combinatorial complexity of possible configurations presents a major computational challenge. To address this challenge, the material selection problem is formulated as a Quadratic Unconstrained Binary Optimization (QUBO) model and is solved using the Variational Quantum Eigensolver (VQE) and Quantum Approximate Optimization Algorithm (QAOA). By mapping OLTARIS dose-equivalent data to the Ising model and utilizing the quantum-classical hybrid approaches of VQE and QAOA, optimal shielding configurations that minimize radiation dose are identified, demonstrating the potential of Quantum Algorithms in advancing space radiation protection strategies. Our results are in agreement between OLTARIS and Quantum Optimization in the SPE environment.