## 2 Materials and Methods
### Three-Dimensional Printing Technology Applications in Outpost Construction
The diameter, length, and volume of the inflatable module were 2.5 m, 8 m, and 40 m\({}^{3}\), respectively. The printing machine was a large plotter capable of spraying the liquid binder on the regolith (Figure 9 (right)). To print each building component, firstly, the corresponding 3D CAD file was given to the machine. Then, the 3D body of the component was dissected by some horizontal planes to create 2D sections. Finally, each 2D section was sent to the plotter to print the section. This process continued until the whole body of the component was printed. In [PERSON] et al. 's study, the location of the lunar outpost was proposed on the Moon's south pole, where the presence of water was already reported by different researchers [3; 4; 5; 89; 90; 91]. As already mentioned, [PERSON] et al. expressed that the thickness of each printed component can be selected between 1.5 m and 2 m to curtail solar winds. Moreover, they stated that the thickness of printed components must at least be 0.8 m to protect the outpost from meteorite impacts. The main challenge in [PERSON] et al. 's outpost was the potential for evaporation or the binder liquid becoming frozen when it was sprayed on the regolith layer in vacuum and cryogenic temperature conditions. To evaluate this challenge, some experiments were conducted in the laboratory setting under vacuum and very low temperature conditions. It was found that the impact of cryogenic temperature on the liquid binder is more critical than the vacuum condition. However, it was concluded that the binder liquid survives if some necessary specifications are considered. In addition, a preliminary estimation of the transportation cost showed that for the construction of the 40 m\({}^{3}\) volume outpost, the interplanetary transportation of 3.8 tons of liquid binder together with 1.5 tons of inflatable module is needed. The transportation cost per kg is variable for different  
Figure 8: The dome-shaped lunar habitat manufactured using contour crafting 3D printing technology [9]. planets and space mission purposes; however, an average estimate can be EUR 200,000 per kg. Hence, the transportation of the whole 5.3 tons of materials from the Earth to the Moon costs at least EUR 1060 billion. In NASA's 3D-Printed Habitat Challenge Competition project [79], two teams, including the AI Space Factory and Penn State University, competed to construct a habitable 3D-printed outpost on Mars. The competition's objective was to develop an autonomous printer that required minimal human intervention and fulfilled rigorous structural tests. The scale of the printed outpost was one-third of the main proposed design. The victorious team would be awarded a prize of USD 500,000 [79]. The AI Space Factory's team constructed a 15-by-8-foot egg-shaped structure (Figure 10a), known as MARSHA (Mars Habitat), using a recyclable composite comprising basaltic fibers and a bioplastic derived from plant starch. The material, heated to approximately 176 \({}^{\circ}\)C, was extruded and quickly cooled, and it transformed into a durable and reusable substance within five minutes. Meanwhile, Penn State's team employed river-sand-based cement to build their structure. This cement had the advantage of setting faster than conventional concrete, resulting in a stronger material. Within 120 min, the cement would solidify and prevent any deformation. The completed structure resembled two interconnected igloos, each featuring a cone-shaped roof (Figure 10b). However, the team encountered a setback when they discovered that the conveyor belt responsible for transporting cement powder had reversed, leading to the extrusion of only water by the printer [79]. To assess the structures' integrity, a series of tests were conducted. Firstly, colored smoke was blown into the structures to reveal any cracks or flaws. Secondly, judges dropped three weighted balls from a height of 4.5 m onto the structures: a 7.25 kg ball, a 9.07 kg ball, and a 11.80 kg ball.