The standard building blocks for the habitat are the hexagonal and pentagonal tiles. There are three standard geometries used to complete the habitat, one hexagonal and two pentagonal. The pentagonal tiles in the smaller pentagonal polyhedrons have a different mating angle than the larger tiles but are the same basic size. The large volume of the habitat has 20 hexagons and 12 pentagons, like a typical soccer ball. The smaller volumes are platonic solids made up of 12 pentagons to form dodecahedrons (the common 12-sided die).
All the tiles are made from the same materials, use the same reinforcement technique and are approximately 16 inches thick. Most of the volume of the tiles is a mixture of polyethylene powder and Martian regolith. This material will be pressed into a mold and heated to approximately 130° C. This process melts the polyethylene and regolith mixture to form a composite. The addition of the regolith reduces the amount of the polyethylene required by consuming some of the volume of the molded part. Using the regolith and polyethylene improves compressive strength while maintaining pliability. Other advantages of using polyethylene are that it is effective at shielding against GCR (galactic cosmic rays) and has good wear resistance. Its typical use on Earth as shot peen masking demonstrates its effectiveness as protection against high velocity small particles such as rocket motor ejecta.
Because of the tension force exerted on the tiles when the habitat is pressurized, the tiles need anchoring points to mechanically secure them to each other. To achieve this, the press tool has provisions for basalt fibers to be wound through the internal volume of the tile before the polyethylene and regolith are pressed. An insert, molded from polyethylene, is used to help reduce the bend radius. These windings act as anchoring points to distribute the load throughout the tile and help to strengthen the tiles against impacts. Finally, the border of the tile has polyethylene strip molded into the tile to act as a weld area for sealing the habitat. These features can be seen in the images below. More research on the appropriate mix ration of plastic to sand and fiber is need, additionally, more work is needed on winding patterns.
The Mechanical Electrical Plumbing (MEP) tile is similar to the basic tile in its construction, except for special inserts in the center of the tile. It has all the same features of the standard tile, using the basalt fiber windings and the polyethylene inserts for welding. The same mold tooling can be used to create this tile by utilizing a mold insert to create space in the center of the tile for the MEP inserts. The fiber windings go around the MEP insert and are still used as mechanical reinforcement for the pressure retaining aspect of the structure. The MEP inserts are necessary to provide an avenue for heat exchange of the and provide pass-throughs for electrical, water, and other life support services. A diagram of a MEP tile can be seen below.
The hatchway tile is very similar to the MEPS tile in construction. An aluminum support structure is used frame the hatchway and bear the tensile load from the panel. The basalt fiber anchors are wound around the aluminum insert, and a molded polyethylene Insert is used to make the seal to the hatchway. The tile is then sintered in the same method as a standard tile. While each of the three smaller cells have a suit hatch tile, it is only used for emergencies in the Bio-Generation and Multipurpose Cells.
The viewport tile is once again constructed in a similar method as the standard tile. It utilizes the same design features as the standard tiles. Using a mold insert, a viewport is added to the center of the tile. The basalt fiber winding wraps around the parameter of the viewport insert. The fiber windings support the insert and help to retain it in place. The viewport tiles are used in the Bio-Generation Cell to allow sunlight into the habitat. A viewport tile can be seen below.