## 3 Results and Discussion  
In the previous sections, a detailed review of extraterrestrial physics-based challenges, regolith aggregate ability, and the potential techniques for constructing extraterrestrial outposts on the Moon and Mars was presented. In this section, a discussion of the main challenge pertinent to planetary habitat development is provided. Amongst physics-based challenges, the cryogenic temperature appears to be the most pressing problem for the development of extraterrestrial outposts. For instance, regarding the location of the outpost on the lunar surface, it may be said that the Shackleton crater, situated in the southern pole, is appropriate for outpost construction. In this region, the sun never sets, and it shines at a relative horizontal angle relative to the crater's surface [20]. Thus, minor solar radiation reaches the outpost. Nevertheless, the main problem will be the cryogenic temperature derived from the polar nature of the region. Therefore, ultra-resistance to cryogenic temperatures must be regarded as a key criterion in the selection of materials and 3D-printed modules. The regolith found on the Moon and Mars can be applied in both raw and synthesized forms. The raw regolith can be used as a shield layer to protect the outposts from meteoroid impacts, solar radiation [110], and temperature fluctuations. It can also be directly deposited on the outpost and covered with membranes for guaranteeing the stability of the walls. Inthis case, the geomechanical properties of the regolith are highly influential with respect to the wall's stability [10,111]. On the other hand, the synthesized regolith can be combined with additives or binders to create new materials with increased compressive strength. The physical and geotechnical properties of the raw regolith are also very seminal in the 3D printing process. During the manufacturing process, the regolith must be collected by rovers and is fed into the printing machine; hence, the subsequent factors must be considered. Firstly, collecting surficial lunar regolith needs more robotic energy than Martian regolith. In fact, from the Moon's surface level to the depth of 30 cm, the regolith's bulk density increases from 1.30 g/cm\({}^{3}\) to 1.69 g/cm\({}^{3}\)[112,113]. By contrast, on Mars, the regolith's bulk density builds up from 1.30 g/cm\({}^{3}\) (at surface) to 1.34 g/cm\({}^{3}\) (at depth = 30 cm) [114]. And more than this, the geotechnical properties of the Martian regolith are much closer to the lunar mare regions rather than the lunar highlands. The reason is that in a similar way to the Martian environment, the lunar mare regions have been impacted less by the meteoroids compared to the lunar highlands. Thus, the construction of a prospective outpost in mare regions requires less robotic energy as the regolith's bulk density is closer to the Martian regolith. The second consideration is related to the slope stability of the regolith's slopes; as the gravity of the Moon is less than Mars, the regolith's slopes remain stable, with sharper angles between their toe and the horizon. This matter also has a direct impact on the thickness (and volume) of the regolith required to be deposited on the outpost. The third consideration is pertinent to the effect of temperature fluctuations on the water volume contained in the regolith. The stress cycles derived from temperature fluctuations perpetually alter the physico-mechanical characteristics of soils [115, 116, 117]. Since hydro-mechanical coupling between the solid skeleton of the regolith and its frozen water continually shifts [118], the effect of temperature on poroelastic parameters must be also taken into account. The inflatable modules are the most appropriate options for providing the breathable environment inside the habitat while 3D printing technology can be used for manufacturing the outer building components. The inflatable modules provide numerous benefits in the construction process.