air leakage, as the habitat would be fully sealed from the outside except for a few exits to the surface. These underground habitats would be akin to bunkers\fallout shelter The construction of an underground habitat would probably be more complex; one of the first machines from Earth might be a remote-controlled excavating machine. Once created, some sort of hardening would be necessary to avoid collapse, possibly a spray-on concrete-like substance made from available materials. A more porous insulating material also made in-situ could then be applied. Rowley & Neudecker have suggested "melt-as-you-go" machines that would leave glassy internal surfaces. Mining methods such as the room and pillar might also be used. Inflatable self-sealing fabric habitats might then be put in place to retain air. An alternative solution is studied in Europe by students to excavate a habitat in the ice-filled craters of the Moon. Underground farming Farms set up underground would need artificial sunlight. As an alternative to excavating, a lava tube could be covered and insulated, thus solving the problem of radiation exposure. Surface habitats A possibly easier solution would be to build the lunar habitat on the surface, and cover modules with lunar soil. The lunar soil is composed of a unique blend of silica and iron-containing compounds that may be fused into a glass-like solid using microwave energy. Blacic has studied the mechanical properties of lunar glass and has shown that it is a promising material for making rigid structures, if coated with metal to keep moisture out. This may allow for the use of "lunar bricks" in structural designs, or the vitrification of loose dirt to form a hard, ceramic crust. A lunar habitat built on the surface would need to be protected by improved radiation and micrometeoroid shielding. Building the lunar base inside a deep crater would provide at least partial shielding against radiation and micrometeoroids. Artificial magnetic fields have been proposed as a means to provide radiation shielding for long range deep space crewed missions, and it might be possible to use similar technology on a lunar habitat. Some regions on the Moon possess strong local magnetic fields that might partially mitigate exposure to charged solar and galactic particles. In a turn from the usual engineer-designed lunar habitats, London-based Foster + Partners architectural firm proposed a building construction 3D-printer technology in January 2013 that would use lunar regolith raw materials to produce lunar building