Radiation Shielding

Any moon base will likely have to utilize local resources to support itself. Water can be harvested from ice hidden deep in craters, the possibility of mining the moon for metals also exist. Why not harvest the materials for our radiation protection from the moon? Present in vast quantities across the lunar surface is what we call regolith. Across the moons many millions of years of existence, the rocky surface has been weathered down by the solar wind, impacts, and other such events. This has left much of the surface covered in a fine layer of regolith, a mixture of dust, rock particulate, and other ground down minerals. Regolith is incredibly fine, and can cause issues with equipment due to its fine nature, the regolith often sticking to much of what it comes in contact with. Should it be tracked into any human habitat, it could even cause problems with human health. However, due to its abundance, it can be utilized and turned useful, rather than continue to be a minor hindrance to our habitation efforts.

When it comes to shelter, a possible lunar habitat has many options. We can build modules either on Earth or in orbit, then deploy them to the surface in sections, similar to how the ISS is constructed. We could also use inflatable habitats, in essence tents, formed and held by an internal supporting structure and atmospheric pressure. Both of these options, which are the most likely type of structure we would deploy, would be located out on the surface of the moon, among the regolith. To take advantage of the local abundance of materials, we could essentially bury these structures within the regolith itself, digging out pits to place our structures, then covering them with the excavated regolith. This process could further be enhanced by the usage of drones and other unmanned vehicles, deployed months ahead of human arrival, to prepare the subsurface layout of the base, and to assist humans in setting up their habitation modules and burying them. Other construction methods could include utilizing lunar soil in a form of 3-D printing, in which case we could possibly construct shells of our radiation shielding regolith, then inflate our structures within to form our habitats. 

Building off current/former studies into the concept, our regolith layer would need to be around 50 centimeters at a density of 1.5 gm/m^3.  This should provide adequate protection from the normal background radiation that poses the largest long term health risks to human habitation. With on average, a thickness of five meters before yielding to the crust of the moon, there should be no shortage of material to utilize in this effort. Additionally, our regolith layer would serve as a thermal barrier, assisting in heat retention inside the base. We can also further enhance the shielding properties of regolith by layering the material with other radiation shielding/absorbing materials, such as aluminum.

Below is a possible layout for a buried design, with all necessary facilities protected by a thick shell of regolith.

While water and lead have their advantages, their disadvantages are high, and while keeping cost effectiveness in mind, are not entirely practical. To help protect from increased radiation levels should the worst happen, we can dig further into the crust of the moon underneath our base. Around 3 meters below ground level should be sufficient to protect from most natural phenomena that would cause a spike in radiation levels, and we can further increase this margin of safety by surrounding these emergency shelters with layers of lead, or by digging deeper should a larger safety margin be desired. With these shelters designed for uses in extreme emergencies, and with them likely having a small relative footprint compared to the size of our base, shipping up the needed lead, while expensive, should not prove as immense a challenge than if we were to utilize lead shielding for the entirety of the base. To further enhance shielding, we could attempt to surround these shelters with layers of concrete as well, perhaps even a mixture using regolith to utilize available materials, given its effectivness against all forms of known radiation.

With regolith's natural messiness, there are few alternatives besides strict cleaning and maintenance practices. Air locks can be equipped with pressurized air hoses to blow the regolith off into collection receptacles for later use, or perhaps a form of vacuum hoses to suck up the regolioth. With equipment such as rovers, cameras, etc., there is only one identifiable option. Our astronauts/colonists will have to maintain a strict cleaning and inspection regimen, and an adequate supply of spare parts will either have to be shipped to the base regularly, or the base must be outfitted with the capability to locally manufacture spares.