| Lunar Engineering with Non-Metals by Dave Dietzler 2009 At the Moon Society St. Louis chapter we have several mechanical engineers as members. They have broken the mold when it comes to domes and cylindrical or sausage shaped pressure modules and designed box shaped modules made of plate iron. Their calculations show that these modules will have high safety margins if pressurized with a 5 psi (3psi O2, 2psi N2) atmosphere. Their reasoning is that flat plates of iron will be much easier to cast and/or roll than curved and hemispherical plates of metal on the Moon. I've given a lot of thought to metal production on the Moon. Iron and magnesium are two metals that can be produced without upported chemicals on the Moon. Silicon might be obtained without chemicals if it is possible to use serial molten silicate electrolysis to get it separately from iron and purify it with vacuum distillation and zone refining. Sodium, potassium and phosphorus should boil out of the melt during magma electrolysis as impurities in the resultant oxygen along with some sulfur. Barring the advent of an all-isotope-separater, titanium and aluminum production will require upported chemicals, at least until we mine substantial amounts of carbon and chlorine. Chlorine would most likely be roasted from millions of tons of volcanic glass and there's a long shot possibility that it might be present in volcanic gas if we ever drill into intact pockets of volcanic gas in the Moon should they exist. There are other materials available on the Moon that don't require upported chemicals to produce and are just as valuable as metals such as cast basalt, glass, cement, plaster and titanium dioxide. Cast basalt bricks, blocks, beams, studs, slabs, bottles, jars, pipes, ducts and fibers will have many uses and this material can be produced simply by melting mare regolith in solar or electric furnaces and pouring it out into molds or drawing it thru dies. Glass might be made by acid leaching of regolith but it might also be boiled out of highland regolith in furnaces at 1500 C. and higher. Plain highland regolith melted and cast might make a high alumina glass with an unknown degree of transparency. Perhaps magnetic removal of iron bearing minerals from highland regolith followed by melting and working will yield reasonably transparent glass. What could be simpler? Glass too can be used for bricks, blocks, bottles, jars, pipes and fibers. Cement can be made by roasting highland regolith at 1800-2000 K. to drive off silica and other low bp substances to get a CaO and Al2O3 enriched cement. One part of cement can be mixed with two parts of sand (raw regolith screened to the right particle size) and three parts gravel obtained by screening regolith and/or melting regolith and busting up the solid material to make gravel and the result is concrete. Concrete could be mixed with water and poured in large pressurized inflateable modules to make cylinders with walls several feet thick and domed end caps to make concrete habitat modules. * These might also be reinforced with glass fibers for improved tensile strength and the walls could be thinner, thus less concrete would be needed. This would be done in pressurized upported inflatables to recover water vapor as the cement dries. Water would come from volatiles harvesting. The Mark 3 miner could produce over 200 tons of hydrogen a year and when combined with 1600 tons of oxygen from magma electrolysis and ilmenite reduction with hydrogen we could get 1800 tons of water-enough to make a hell of a lot of concrete. Since cured concrete contains about 5% water by weight, this much water could make 36,000 tons of concrete!** Plaster could be obtained by sulfuric acid leaching of calcium rich highland regolith. Sulfuric acid would be made from lunar sulfur, water and oxygen in addition to plain regolith as a catalyst. Plaster, calcium sulfate, is used as a cement setting time retarder and also can be used for dry wall, medical and dental casts, and molds for casting aluminum and magnesium. Titianium dioxide can be obtained by subjecting ilmenite seperated electrostatically from mare regolith to hot hydrogen gas. The result is a mass of particles of TiO2 fused with iron. The iron could be boiled off in the vacuum in solar or electric furnaces to get pure TiO2. This ceramic melts at about 1800 C. and is highly reflective. It could be used to line metal smelting and glass melting/basalt melting furnaces, as a secondary reflector for solar thermal concentrators and for heat shields. Titanium dioxide bricks, blocks, tiles, reflectors and heat shields would be made by sintering the TiO2 particles together in upported graphite molds with solar or electric heat to make solid items. Tanks of LOX and other lunar materials could be launched with mass drivers or rockets. With TiO2 heat shields they could aerobrake into LEO to supply space stations and orbital fuel depots. Concrete habitat modules could be fitted within with concrete slab floors, air ducts and plumbing made of basalt, glass and/or concrete tubes, brick and plaster walls; bath tubs, sinks, shower stalls and planting boxes made of bricks, glass windows, and furniture made of cement. Unlike iron modules there will be no problem with internal wall rusting. The concrete modules would be buried and immersed in the constant sub-selene temperature of minus 20 C. or minus 4 F. thus they will not endure thermal cycling that would lead to cracking. Life inside will be more like life inside a brick house with plaster walls; whereas iron modules with iron bulkheads would seem like the inside of a submarine. Iron walls would have to be welded in and out or bolted in and out. Brick and plaster walls can simply be knocked down with hammers when it comes time to remodel and reasign space. While abundant concrete will make lots of modules for living, iron modules will be better for working. Heavy machine tools will need sturdy bases and they will set up vibrations and shock forces that would lead to cracking of concrete modules. So it seems the most productive strategy on the Moon will be to use all available materials for the purposes they are most suited to for the sake of functionality and economy. Iron modules will not rust on the outside but they might rust on the inside, weaken and rupture. We must upport some paint to prevent rusting of iron work modules. Iron modules will also be buried to protect them from thermal extremes on the Moon. One last word about glass. Pure silicon dioxide, silica, can be mixed with sodium and potassium oxide to lower its melting point and make it more easily worked. Glass lenses can collect sunlight and focus in onto bundles of glass fibers to pipe light into modules during the lunar day. Fiber optic bundles can also be used to transmit modulated laser light for telecommunications. Let's not forget that basalt and glass can be used for dinnerware and pottery. We won't have to eat from metal mess kits alone! *Since gas pressure wants to swell up into a spherical shape curved and domed concrete modules will be stronger than box shaped concrete modules ** see: http://www.nss.org/settlement/nasa/spaceresvol3/cemncon1.htm |
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| Note: http://hypertextbook.com/facts/1999/KatrinaJones.shtml concrete denisty = 150 lbs./cubic ft cylinder 20 ft wide and 100 feet long, walls two ft. thick 12,560 cubic ft 1,884,000 pounds 942 english tons with domed ends, estimate 1100 tons and with one year's output of a Mark 3 miner we get enough H2 to make 36,000 tons of concrete..... |
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