Sintered Brick Construction
Sintered Brick Construction
If construction of an enclosed space can wait until there is a little industry established upon Luna, then a roof can be supported by locally produced sintered regolith brick with locally produced fiberglass reinforcement. Step 1: Dig a ditch with a bottom semicircular in cross section and sized to contain the desired building. Step 2: Place a circular construction frame at the end of the ditch. Step 3: Place sintered bricks in frame to form a circle of bricks that have been shaped for making that size circle. Step 4: Band the circle of bricks together with several turnings of fiberglass cord that fit in preformed notches on the outside of the bricks. Step 5: Remove frame from brick circle and tamp regolith between brick circle and bottom of ditch. Step 6: Use brick circle as a frame for adding inner brick circle one half brick further down the length of the cylinder with its own reinforcing fiberglass cording using bricks specially sized for the inner layer. Start the longitudinal reinforcing cables that are preterminated in fittings for the eventual door sections. The longitudinal cables run in notches preformed on the inner surface of the outer circle bricks. Add alternate inner and outer brick circles until the ditch is full of a brick cylinder. Add door sections at the cylinder ends and cover the structure with regolith. Spray the interior with a layer of locally produced liquid glass and then with a layer of locally produced liquid aluminum. Then fill the building with atmosphere. This building could be built entirely by remotely operated devices and will not collapse from a mere loss of atmosphere accident.
Spraying liquid glass might not work for making a gas tight seal on the moon because liquids in general are not stable in a vacuum. The best one could hope for is that a liquid would evaporate only slowly because of a very low vapor pressure for equilibrium of that liquid. As an alternative to "Spray[ing] the interior with a layer of locally produced liquid glass", one could first be sure that the surface of each brick that ends up on the inside surface of the cylinder is a gas impermeable surface such as is achieved by glazing. Where interior bricks meet neighboring bricks the edges should be beveled. This leaves a groove between each row of bricks. Then to finish the gas tight seal for the whole cylinder, a bead of glass heated to the softening point is forced into this groove where it sticks to the brick surface and is left to harden. An important point is that one or another process for lunar development will not work as imagined, but when this is discovered in testing alternative methods should be developed.
The atmosphere contained in a building might be air, hydrogen, nitrogen, oxygen, helium or argon depending upon the industrial use to which the building will be put. Naturally personnel must wear self-contained isolated breathing apparatus (SCIBA) when working in buildings with non air atmospheres. A reason for a non air atmosphere in a building would be the use of the building to construct devices intended for service in the ambient lunar vacuum which devices contain electrical or structural alloys that would corrode in an air atmosphere. Sodium could be used as an electrical conductor or as a solder on equipment for vacuum service as long as the temperature of the equipment is kept low enough that sublimation of the sodium does not become a problem. Sodium would probably be put to such use in alloys so that if sublimation did occur to any substantial extent, a film of the other alloy elements would form to stop the sublimation. SCIBA equipment would include rebreathing technology to prevent exhaled air and moisture from entering a building's atmosphere. SCIBA would also be useful in titanium metallurgy, in which casting can be done in an argon, hydrogen or helium atmosphere. Argon would be preferred for lower thermal conductivity.
When Should People Arrive?
The ability to use various locally available resources (ISRU) to support human life suggests that it would be better for people to arrive on Luna after these resources become fully available. This can be the case if industry is initially established by remotely controlled manipulators and other devices (See Bootstrapping Industry). If one considers the inconvenience (from management's point of view) and expense of working with remote controlled manipulators with a three second response time as compared to the inconvenience and expense of providing air, food and water costing more than its weight in gold to employees on Luna; then one might see the logic in developing local life support resources before the first people arrive, rather than shipping supplies from Earth. As local life support resources become more easily available the cost of people on site will decrease; and as the level of capital goods investment increases, the value of humans on site will increase. So as development continues more people on Luna will take over tasks for which the problems of remote operation are especially bothersome.