Tires for Mars Rovers: Reinforcing BR and BR/ Vinyl-Methyl Silicone Rubber Compounds with Carbon Black, Nano-CaCO3, or Silica for Good Low- Temperature Dynamic-Mechanical Performance

Dynamic increment in Mars exploration missions necessitates the development of new materials that can satisfy the ever more stringent requirements. Currently, most of the materials used for manufacturing Mars rovers and landers are based on various metal alloys that provide high reliability in the Martian environment. However, the future planned missions, including the first human crew landing on Mars, require the development of new rubber materials that could be used for sealing Mars suits, for tires/tracks, and for damping systems for heavy Mars rovers. This research aims to investigate the properties of butadiene rubber (BR) and butadiene/vinyl-methyl silicone rubber blends (BR/VMQ) filled with various reinforcing fillers: carbon blacks (CBs), silicas, and nanometric calcium carbonate (nanoCaCO(3)), in order to evaluate their performance from the point of view of Mars' environmental applications. The study revealed that the designed composites exhibit very good low- temperature elasticity, and the addition of 30 phr of high surface area CB (N220) or silica (Ultrasil 9100) results in good mechanical properties of the compounds. The mechanical properties of the BR/VMQ blends depend on the type of reinforcing filler. The addition of the CBs resulted in better mechanical properties, while the incorporation of silicas worsens the mechanical properties of BR/VMQ blends in comparison to their BR counterparts. The high- cis BR grade exhibits a strong tendency to crystallize in the operating temperature range on Mars (crystallization similar to- 60 degrees C, melting similar to-20 degrees C), and the addition of the fillers nucleates the crystallization, resulting in a higher amount of the crystalline phase. This might be a serious problem for any sealing application of the rubber compounds. For this reason, a non- crystallizable BR grade is recommended for further studies.