5.6. Materials production
Bricks and cement
Clays, abundant at least in some areas (especially on the oldest Southern hemisphere surface), will allow to make bricks, an excellent building material. To get the best quality, we should push cooking heat up to 900° C, but a temperature of 300° C might be enough; this relatively low level would allow considering, for heating the furnace, using the heat produced by the nuclear power generators (the Sabatier reactor does also operate at this level). The Homestead Project engineers proposed the extensive use of bricks for the construction of underground enclosures. The idea is appealing because it would avoid the production (or import) of large metal modules, but it is unrealistic in terms of labor consumption: manual assembly of buildings, moreover wearing spacesuits! Unless we prefabricate elements of walls and vaults in a pressurized workshop…
On the other hand, it is possible to manufacture good mechanical quality cement from Martian soil, which is loaded with salts (magnesium sulfate, sodium chloride) and rich in clays. Wetting the soil after drying we can get a material (duricrete) offering the same resistance as concrete but more sensitive to fracture, a defect that can be corrected by adding fibers into the mixture. From this material all kinds of building elements could be cast, as if using concrete.
Another particularly attractive possibility is the use of plastics, for manufacturing either inflatable envelopes or structural elements such as beams, angles, partition walls, and so on. Indeed, it is easy to produce ethylene from hydrogen and carbon monoxide, itself a byproduct of the production of oxygen by thermic decomposition of CO2 or obtained using a similar reaction to that of Sabatier:
3H2 + CO2 -> H2O + CO + 2H2
For this purpose we would use the following reaction (highly exothermic and enjoying a high equilibrium constant, therefore a good yield):
2CO + 4H2 -> C2H4 + 2H2O
Ethylene is the basis for the production of the majority of the most commonly used plastics, especially polyethylene, polypropylene, polycarbonate (for windows), polyester resin. This production line will allow expanding the products range of the colony far beyond building materials: fabrics, lubricants, insulating materials, various tools, packaging, containers, etc. Polyethylene is easy to handle and store because it liquefies at Martian night temperature and can be stored as a liquid under a few bar pressure.
It should be stressed that it is the presence on Mars (unlike the Moon) of both carbon and hydrogen that will allow the development of this « industry », critical for the development of a colony.
Glass and ceramics
Mars clays should enable the manufacture of ceramics, while silica, ubiquitous, will allow producing glass. One problem though: the Martian silica will be obtained from a sand rich in Fe2O3 iron oxide (hematite) that we must get rid of if we want to get a good optical quality glass. This can be done by reducing Fe2O3 with carbon monoxide and segregating the iron thus obtained. From glass, we can also manufacture glass fiber, useful for elaborating composites.
The need of steel is what will trigger the quantity of iron to be extracted from the Martian ground, glass being rather a byproduct. In fact, two reactions can be implemented to reduce Fe2O3: the one mentioned above, using carbon monoxide and another one using hydrogen; in the latter case, hydrogen can be recycled from the electrolysis of the water produced by the reaction. For the Moon, a similar process has been proposed, but it was to be applied on ilmenite (FeTiO3, though more difficult to reduce). Carbon and other metals such as nickel or manganese, all present on Mars, should be added to resulting iron in order to get all desired steel varieties. Carbon will be preferably supplied from carbon monoxide, but it could also be from plant waste otherwise lost.
Steel will play an important role in the establishment of the colony, for structures but also for making various tanks, tools resistant parts, machinery, vehicles… Note that in the presence of an atmosphere containing no oxygen and minimal amounts of water vapor, steel will practically be “naturally” stainless.
Fe2O3 oxide being everywhere in the Martian ground, and in high proportions, mining will not be difficult.
Aluminum is also present in the ground (4 % in terms of mass), but in the form of alumina (Al2O3) the reduction of which is difficult and requires a lot of energy (20 kWh per kg of aluminum).
Reduction can be done by electrolysis, at around 1,000° C, of an alumina solution, with carbon electrodes (made locally). Given the good resilience of steel within the Martian atmosphere and the high energy cost, aluminum will be used only for a few special applications to take advantage of its lightness (flight parts) or its good electrical conductivity (cables). For the latter purpose, copper would be better. But if its oxides are easily reduced, the element is scarce. We’ll find it in operable quantities only in ore deposits that we will have to find. The high volcanic and hydrothermal activity of Mars in the past leads us to think that, generally speaking, there should be many metals deposits.
5.7. Semi-finished products production
It is, as soon as possible, necessary to enable the colony to produce, from basic materials, the semi-finished products necessary for its extension and maintenance needs. This implies importing machines and transformation tools from Earth.
The Homestead study attempted to establish an inventory of these means but at a growth scale about 10 times slower than that we consider in this study (up to +18 settlers each synodical revolution, versus +200) . Nevertheless, we may refer to it to get an idea of the range and scope of these infrastructures. Here are these estimates multiplied by10, for rescaling:
Consumption of raw materials listed below (mT/year):
- cement: 2000
- glass: 750
- polyethylene: 500
- polycarbonate: 350
- polyester: 300 (composites)
- steel: 750-1500
- aluminum: 100
Clay or cement semi-finished products:
- bricks, blockworks
- panels and precast beams
Metal semi-finished products (steel and aluminum):
- Sheets, pipes, tubes, cables, wire cloth
- shells, beams, wheels (by stamping)
- beams, valve bodies, parts of planetary vehicles… (by casting)
Plastics and glass semi-finished products:
- molded-items: packaging, containers, various utensils
- polycarbonate panels: porthole panes, domes
- polyester: castings, draped or coiled elements in glass-resin composite
To these basic products, settlers will have to add:
- treatment processes requiring specific means (baths, ovens): galvanizing, powder-based coatings, electroplating
- machining means: drill, precision lathe, milling machine, grinder, cutter
- welding means, plasma cutting
- handling means: bridge, manipulating arm
- fast prototyping device
The study estimates the details of volumes and masses of corresponding materials (to be imported from Earth). This gives totals, also increased by a factor of 10 for scaling, of approximately:
Volume: 1,000 m3
mass: 65 mT
These values suggest, if we refer to cargo traffic assumptions, that the volume to be transported for the initial setting up of these means of production will be more constraining than the mass itself. And this, all the more than civil works means, already mentioned, will have to be added up (scrapers, excavators, trucks …). We will therefore be compelled to consider either to dedicate one or two unmanned preliminary missions to lay these materials on the surface of Mars, or to accept a progressive increasing of the layout tempo of the colony over several synodical revolutions.
5.8. Recap of main means
|Interplanetary traffic||12||orbital shuttles- 50 flights per synodical revolution|
|Planetary traffic (staff)||10||rovers, 50 jeeps, a few hoppers and drones|
|Electricity Generation (for 160 MW)||20||nuclear generators of 8 MW each (6 T, Tturb= 1800 K)|
|Habitats||700||modules of 5×20 m² + 30 common areas of 1000 m²|
|Greenhouses||6 ha||hydroponics, artificial lighting (100 MW)|
|Animal husbandry (?)||50 000 fish, 700 goats, 2700 hens|
|Water (hab.& greenhouses)||6 to 10 MW||for 24 to 36 mT/sol1, ground heating, by microwaves|
|Oxygen||7.3 MW||for 28 mT/sol (electrolysis process hypothesis)|
|Hydrogen||4.6 MW||for 2.2 mT/sol, electrolysis|
|Methane||1.3 MW||for 6.2 mT/sol, Sabatier (CO2,H2) + electrolysis|
|Production of Materials:|
|Cement||2,000 mT/year||from soil loaded with salts and clays, in ovens|
|Plastics||1,100 mT/year||from polyethylene, obtained by Sabatier (CO2, H2)|
|Glass||750 mT/year||from silica, in high temperature ovens|
|Ceramics||from clays, in high temperature ovens|
|Steel||750 to 1500 mT/year2||from hematite Fe2O3, reduced by CO ou H2|
|Aluminium||100 mT/year||from alumina Al2O3, electrolysis at 1000°C|
|Semi-finished products production:||65 mT, 1 000 m3||of machines and tools|
|Bricks||clays / molds and ovens 300°C (900°C prefered)|
|Concrete blocks, beams||cement / molds and ovens|
|Fiberglass||glass / ovens, spinneret|
|Sheets, plates, tubes, cables||steel, aluminum / rolling mill, spinneret, cutting machine, bending machine|
|Shells, beams, wheels||steel, alu / stamping machine|
|Molded parts||steel, alu, glass / ovens and casting molds|
|Various plastic parts||polyethylene, polycarbonate / molds, cutting machine|
|fiberglass, polyester / molds, ovens|
|Finishing||machining workshops, surface treatment, welding|
|Number of active sites||4||for water & regolith, ores (2), clays|
|Number of machines / site||2||of which 1 only active at all time|
|Number of trucks / site||2|
|Installed power / machine||500 HP rate used : 25 %|
|Installed Power/truck||200 HP rate used : 25 %|