The discovery of radiation-shielding materials remains a critical technology to enable long-term space travel and extraterrestrial colonization. Hydrocarbon polymers, such as high-density polyethylene (HDPE), are among the best radiation attenuators due to their rich H content and lightweight. Due to their simple chemical structure that lacks larger heteroatoms, HDPE is also resistant to numerous radiation-induced degradation pathways that often limit the applicability of more sophisticated polymers. One drawback of hydrocarbon polymers is their inferior mechanical properties, such as tensile strength and impact toughness, relative to metals and other high-performance polymer systems. In this report, we develop an alkylated reduced graphene oxide that is used as an additive to enhance the storage and tensile moduli of HDPE by 10-15% across the lunar temperature range. These additives outperform unmodified reduced graphene oxide by 30% due to better dispersion through the polymer matrix as observed by cross-sectional scanning electron microscopy. POLYM. ENG. SCI., 2019. (c) 2019 Society of Plastics Engineers