<p>This study investigates the performance and molecular stability of ultra-high molecular weight polyethylene (UHMWPE) fiber-reinforced hydrogen-rich polybenzoxazine composites exposed to the space environment on the International Space Station (ISS). The composite is designed specifically for spacecraft applications requiring lightweight radiation shielding against galactic cosmic rays and solar particle events. Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), dynamic mechanical analysis (DMA), and short beam shear testing were used to evaluate both surface degradation and bulk property retention. Chemical degradation due to direct sunlight exposure is limited to the uppermost 30&#xa0;nm of the composite surface, with formation of hydroxyl and carbonyl groups. No significant changes in the glass transition temperature (<i>T</i>_g), short beam shear strength, or density are observed between space-exposed and control samples. Thermoluminescence dosimetry data indicated significant attenuation of incident radiation. This study confirms the potential of the UHMWPE composite material for use as a multifunctional structure and radiation shield for extended space missions.</p> Graphical Abstract <p></p>