A lunar base with an inflatable module.
Conceptual drawing. There have been numerous proposals regarding habitat modules. The designs have evolved throughout the years as mankind's knowledge about the Moon has grown, and as the technological possibilities have changed. The proposed habitats range from the actual spacecraft landers or their used fuel tanks, to inflatable modules of various shapes. Early on, some hazards of the lunar environment such as sharp temperature shifts, lack of atmosphere or magnetic field (which means higher levels of radiation and micrometeoroids) and long nights, were recognized and taken into consideration. Some suggest building the lunar colony underground, which would give protection from radiation and micrometeoroids. This is not the only advantage to this option. The average temperature on the moon is about −5 °C. The day period (two weeks) has an average temperature of about 107 °C (225 F), although it can rise as high as 123 °C (253 F). The night period (also two weeks) has an average temperature of about −153 °C (−243 F). [41] Underground, both periods would be around 24 °C (75 F), and humans could install ordinary air conditioners. [42] The construction of such a base would probably be more complex; one of the first machines from Earth might be a remote controlled boring machine to excavate living quarters. Once created, some sort of hardening would be necessary to avoid collapse, possibly a spray-on concrete-like substance made from available materials.[43] A more porous insulating material also made in situ could then be applied. Inflatable self-sealing fabric habitats might then be put in place to retain air. As an alternative to excavating, it is possible that large underground extinct lava tubes might exist on the Moon.[44] A possibly easier solution would be to build the lunar base on the surface, and cover the modules with lunar soil. The lunar regolith is comprised of a unique blend of silica and iron-containing compounds that may be fused into a glass-like solid using microwave energy. [45] This may allow for the use of "lunar bricks" in structural designs, or the "glassing" of loose dirt to form a hard, ceramic crust. Others have put forward the idea that the lunar base could be built on the surface and protected by other means, such as improved radiation and micrometeoroid shielding. Artificial magnetic fields have been proposed as a means to provide radiation shielding for long range deep space manned missions, and it might be possible to use similar technology on a lunar colony. Some regions on the Moon possess strong local magnetic fields that might partially mitigate against exposure to charged solar and galactic particles.[46]