What's it made of? Part II: Supra-local Supermaterials

If more advanced technologies are available to reduce the cost of transport compared to the cost of extracting resources in the Solar System, it would be wise to consider a more general distribution of resources. 

In today's world, it costs very little to move large quantities of raw materials across the oceans. This has allowed iron from Australia, neodymium from China and lithium from Chile to end up in a Japanese factory. 

Human expansion into the Solar System might eventually create a similar sort of exchange. Resources readily available and easily obtained on one body, such as nitrogen on Triton, can be traded with buyers located on bodies that lack it, such as our Moon. 

With this in mind, it makes more sense to use the Solar System-wide distribution of resources when determining which materials will be used to build rockets and construct space habitats.

Solar distribution of elements

Please expand the image.

Above is a graph representing the relative abundance of the elements. It is logarithmic, so small differences (such as between Helium and Hydrogen) actually mean that Hydrogen is about ten times more abundant than Helium.

A more compact representation.

The most common elements.

Comparing the graphs, we can clearly see that the lighter elements are more abundant, with uncharacteristic dips in the abundance of Lithium, Beryllium and Boron. 

The reason for the dip is related to the fusion product chain in stars, which is another discussion.

Carbon, Nitrogen, Magnesium, Silicon, Iron. These are the six elements that will form the basis for most materials in a system-wide industry. 

Oxygen will be the primary oxidizing agent, Hydrogen the primary reducing agent. Neon is too inert to make anything out of and Sulphur does not form strong compounds.

From these elements, we can produce many of the materials already known for their high specific strength today. These include aramid fibres (carbon, nitrogen), carbon fibres (carbon) and high-strength steels (carbon, iron).

How will these elements be distributed inside the Solar System?

Condensation temperature vs Distance from Sun

The presence or absence of elements in the planetary bodies, asteroids and comets of our Solar System depends on how and where they were formed.

The first disk of gasses and dust that surrounded our young Sun contained a relatively homogeneous mix of elements. It created a temperature gradient across dozens of astronomical units, ranging from 6000K near its surface to near background 3K temperatures at the edges of the system.

Different elements condense (become solid) at different minimum temperatures during planetary formation. The lightest elements are boiled off the inner planets. Ices can only be found readily in the furthest gas giants and comets.

Layers of Titan (Organic: carbon-hydrogen molecules)

The condensation temperatures explain, for example, why there are large lakes of methane and other hydrocarbons on Titan, and suggests that Mercury has the highest percentage of heavy elements in its crust compared to other planets. 

We can conclude from this distribution that inner planets would prefer more metallic construction materials, while outer planets would have an easier time sourcing lighter elements such as carbon for their materials. 

Access to the deeper layers of the planets and moons, or to metal-rich asteroids, might however make this distinction irrelevant. 

Common materials 

What will be the 'bulk' materials used if we consider the factors mentioned so far?

The determinant characteristics for the most common materials will be resource availability, ease of production and features such as recyclability, endurance and multiple uses.

Bauxite mine in Guinea. 

On Earth, iron and concrete were for a long time was the most common materials. Iron was easy to find, and so were the ingredients for concrete. Both were strong, durable materials that could be recycled at the end of their useful lives. Smelting furnaces were a mature technology, while cement was easy to handle. 

In our solar system, it is likely that reinforced concrete, carbon fibre and basalt fibre pykretes will become prevalent.

Reinforced concrete foundations for a house.

Reinforced concrete is widely used today. It consists of regular concrete run through with metal wires that handle tensile forces. In space, it is an energy efficient, low-tech and easily sourced material. Since the metal content of the reinforced concrete is only a few percent, large quantities can be made using only small smelters. Forming concrete in vacuum can make it 25% stronger than the same concrete left to dry on Earth, since very little air remains inside.

Carbon fibre is very strong, lightweight and easy to produce. Many planets and moons will have useful amounts of carbon, such as Venus's atmosphere or the dry ice deposits in Callisto's craters. It has already been used in probes and the Space Shuttle. Its high specific strength greatly reduces the tank mass required to hold a certain quantity of propellant, allowing for greater deltaV than metal tanks. However, it is best to expose the entire production line to vacuum to prevent out-gassing damage, and to insulate the exposed fibres against extreme temperature variations to prolong their useful life. 

Steps for producing basalt fibres.

Basalt fibres need only one ingredient: igneous rock. It is melted into a glass and woven in temperature-resistant, inert and immune to radiation damage fabrics. These can be exposed to direct sunlight and do not suffer from temperature variations. They can replace the steel in reinforced concrete while being four times lighter for the same strength. The fabrics can reach a tensile strength of over 4GPa.

Textile-reinforced concrete.

Basalt-fiber reinforced polymer composite

Mixed in with ice, they can provide a strong bulk material known as Pykrete. This is suitable for colder climates in the outer Solar System or for underground or otherwise insulated construction.

Advanced materials

There are many materials with fascinating properties that can be made using only the most common elements. High specific-strength, extreme temperature resistance or other useful characteristics are the norm. They will be necessary to replace many of the metals alloys with additives we rely on today.

Graphenes:

Graphene monoloayer composites

Graphene alone is extraordinarily strong, a surprise superconductor and is a heat conductor in one direction, and an insulator in the other. It is made purely of carbon, but its formation is quite difficult. Making large quantities is quite a technical challenge, although there are headways being made. 

If graphene remains hard to produce in the near future, it can be instead used alongside other materials to improve their properties. Graphene-reinforced aluminium or titanium, which is only 0.3% graphene by mass, contains a metal matrix embedded with graphene nanoflakes. They gain strength without losing ductility, an important quality for plates you don't want to shatter under stress. 

Graphene can also be used in monolayers grown through Chemical Vapor Deposition between sections of metal to vastly increase their strength. Nickel-Graphine is 180 times stronger than pure nickel, and copper-graphene is 500 times stronger, giving it a better specific strength than titanium. The best part is that these composites are only 0.00004% graphene by weight. 

Carbides:

Compounds of carbon and another element. They form some of the strongest materials currently used, such as tungsten or silicon carbide. If there is sufficient boron available, borides with similar structures can be created, forming exceptionally strong and temperature resistant ceramics. 

Carbides are made by burning a metal oxide in graphite at high temperatures. It is a relatively simple though energy-intensive process. The result is grains of carbide that must be bound together or used to coat another material through vapor deposition. 

Glass nanowires:

20 nanometer diameter silica nanowires.

High purity silicates, if produced with nearly no defects, can be used as wires of nanometer-scale diameters to produce materials with 10GPa of tensile strength. They are four times less dense than steel while achieving several times better strength values. The principal advantage, like their impure versions basalt fibres, is that the building materials (silicates) are widely available. Their main challenge is quality: the maximum length of a useful strand if limited by the number of production defects. 

Metallic Glass:

Also known as amorphous metal, these materials do not have regular atomic structures. This helps preventing cracks from forming and propagating. The technical term is absence of grain boundaries.

Metallic glasses need to be cooled extremely fast to prevent crystallization, but this can only currently be performed on very thin pieces of alloy. Millimeter-thick metallic glasses are 'bulk' or BMGs. Future cooling techniques, maybe taking advantage of the microgravity and vacuum environment in space, will allow for thicker pieces. 

Vitreloy or LiquidMetal is a commercial metallic glass that is is twice as strong as titanium. Magnetic metallic glass has high electrical resistance and magnetic susceptibility, which makes it perfect for electromagnetically-accelerated projectiles and magnetically-manipulated structures, such as self-replacing armor plating or extensible spaceship skeletons. A high elastic limit allows some alloys to absorb many impacts without permanent deformation, which reinforced its usefulness as armor material. BMGs made out of the most common elements might not be as strong as those containing zirconium, tungsten and other elements, but they will have better properties than regular crystalline alloys of those same materials.