On the question of the construction of structures on the Moon.
The rapid space technology development reveals great international interest in possible space colonization. Previous extensive experience related to the Moon leads to further exploration and possible colonization of the Earth’s natural satellite. Currently, landing missions are being developed by many countries such as India (Chandrayaan-2/ISRO), China (Chang’e-3/CNSA), Japan (Selene/JAXA) and USA (NASA). Under the Robotic Exploration of Extreme Environments (ROBEX) project, the Institut für Massivbau, TU Dresden is involved into the investigation of the lunar-concrete manufacturing. One part of the investigation process is the design and calculation of precast elements from “Lunar Concrete” for a lunar outpost under extreme temperature loading.
There are various motivating reasons which could answer the main question: “Why do we need to co-lonize the Moon?” Moon can be considered as an object of solving wide range of the problems. Scien-tific purposes of the lunar base are studying of the Moon, monitoring of the Earth, building of a lunar spaceport, which will be used for lunar flights, daily orbit and investigation of the deep space. Launch-ing from the Moon is much more energy efficient than from Earth in terms of fuel consumptions and launching materials. Many functioning parts of the lunar base better to produce directly in-situ, rather than deliver them from Earth. Finally, solar energy can be efficiently produced on the Moon due to high flux of solar radiation. To sum up, the direction of the Moon colonization are to solve energy, resource and environmental crises on Earth; scientific research and observation; Moon as a transporta-tion hub for distant interplanetary space flights.
To begin the investigation it is necessary to narrow down the extensive amount of parameters and en-vironment conditions. From the civil engineering point of view the main points would be to study on temperature behavior on the moon surface for selected building sites; determination of coefficient of thermal expansion and coefficient of thermal conductivity for lunar concrete material; analysis of thermal fields in concrete panels (e.g. using ANSYS simulation software); derivation of the boundary conditions according to the design of lunar structures; design of joints for precast elements.
During the research process few additional ideas have appeared and are listed in the following descrip-tion. First idea concerns the heat transfer problem. High temperature Phase Change Materials (PCM) could be used to store and release heat according to the high temperature cyclic loadings. Secondly, an additional idea arose of a possible structural design for the lunar outpost. As the regolith soil consists out of very fine particles, it can be dangerous to produce structure with joints due to high penetration possibility. Therefore, the shell structure made out of high-strength textile material Kevlar ,  can serve as a hermetic lower layer. Numerous inflatable structure concepts are reviewed by Benaroya et al.  and deployable structures by Gruber et al.  as well suggest using of textile like materials.
To provide the structural stability hollow four-wall bricks can be used and prestressed with the Kevlar, fiberglass or carbon fiber wire ropes, which have high ultimate tensile strength (Laitila ). The bricks are inserted into the Kevlar structure and separated with the partitions. The advantage of the structure is an easy mounting, no joints have to be installed, thus less difficulty during the erection. In case of the depressurization the bricks structure will be bearing the compression load due to gravity and the weight of regolith shield. The proposed design of the structure is shown in Fig. 1, Fig. 2 and Fig. 3.
Fig. 1: Lunar base design consisting of Kevlar shell with the partitions for the hollow four walls lunar concrete bricks.
Fig. 2: Principle of the bricks connection.
Foto is taken from www.happypet.at “Cubes On A Rope Puppy Toy”.
Fig. 3: Joining of the hollow bricks with the Kevlar wire rope.
In the final contribution of the research, the materials and their properties on the Moon are described, which are necessary for the calculations. Additionally, the lunar regolith simulant JSC-1A is presented and can serve for the future research concerning the lunar-concrete material. The proposed structural types are shown and the possible loading cases and the lunar environmental conditions acting on the structure are listed. Next, the most common methods to define the thermal conductivity coefficient and the coefficient of thermal expansion are presented. These methods are important to show in order to define the material parameters of the lunar-concrete. The temperature distributions on the lunar surface are reviewed, which are found using the different techniques and analytical solutions. Subse-quently, the temperature profiles with the most extreme temperature difference needed for the investigation are selected. For the numerical calculations the problem setup and boundary conditions are described. The analytical models of the heat transfer; cyclic temperature loading and thermal expansion calculations are performed and then compared with the obtained ANSYS program numerical results. The results show that 3,0 m of the regolith shielding is an appropriate thickness in order to stabilize and reduce the extreme temperature fluctuations. Next, for the precast panels joints the requirements are listed and possible design of joints is shown. Finally, another structural type is briefly introduced as well as an idea of the energy control using the phase change materials. For the further investigation, the radioactive boundary conditions and the combined structural and thermal loadings should be considered.
. Benaroya, h.; bernold, l.; chua, k.m.: Engineering, Design and Construction of Lunar Bases. Journal of aerospace engineering. 2002, pp. 33 – 45.
. Gruber, P.; Haeuplik, S.; Imhof, B.; Oezdemir, K.; Waclavicek, R.; Perino, M.A.: Deployable structures for a human lunar base. Science Direct, Acts Auctronautica 61, 2007, pp. 484 – 495.
. Ryan, V.: What is Kevlar? Types of Kevlar. 2011, p. 3.
. DuPont Advanced Fibers Systems: Kevlar Aramid Fiber. Technical guide, 1992, 32 p.
. Laitila, E. A.; Hill, S.E.; Forsell, S.F.: Tensile tests experiments. Michigan Technological Uni-versity, 2005.