Recently, geopolymers, a type of inorganic non-metallic cementitious materials, have attracted considerable attention as an alternative to ordinary Portland cement (OPC) and as an effective pathway to mitigate energy consumption and minimize CO2 emissions. The paper proposes a method of geopolymer design to achieve best mechanical properties of the developed material from the civil engineering perspective. Using a ternary plot, the authors selected specific proportions of geopolymer ingredients which predetermine such properties as high workability, high compressive and flexural strength. In the first stage of the research, a mixture of sand, fly ash, and alkaline activators were used to initiate the polymerization process which allowed to form specimens designated for further tests. The promising properties of geopolymers and the lack of access to OPC on the Moon have led to the consideration of using geopolymers as a building material in the construction of future extraterrestrial bases. The In the second stage, simulant of the Moon regolith was utilized. The achieved results justify the claim that the proposed formulation method of geopolymers, designed for civil engineering applications, is useful both for terrestrial and extraterrestrial applications.