Creating sustainable extraterrestrial habitats is a major step towards humans becoming a multi-planetary species. However, a major barrier to this goal is the cost of transporting heavy construction materials into space.
Lighter alternatives to concrete have the potential to significantly reduce this cost. In-situ construction methods that use regolith and other planetary materials could also significantly lower the overall cost of habitat construction.
Aerogels
Aerogels are a remarkable building material that is incredibly lightweight and strong. They are created by replacing the liquid in a gel with gas, leaving behind a porous structure that is mostly made of air. This makes them very effective at insulating materials, as they can effectively nullify all three methods of heat transfer: conduction, convection and radiation. Aerogels are also extremely durable and can withstand extreme temperatures. These characteristics make them ideal for use in space environments, as they will be able to protect astronauts and equipment from the harsh conditions of outer space.
Another benefit of aerogels is that they can block harmful UV radiation. This is important, as it can prevent damage to underlying components and protect astronauts from the harmful effects of excessive UV exposure. Scientists are currently investigating the possibility of using 3D printing techniques to create insulated structures from regolith-based aerogels. This will allow them to use materials that are available in situ, as well as avoid the need for transporting materials from Earth.
Additionally, researchers have been experimenting with adding LHS to aerogels in order to enhance their mechanical properties. They found that the addition of LHS resulted in a linear increase in the Young’s modulus, which is directly proportional to a material’s resilience to deformation. This indicates that LHS can act as a reinforcement to improve the mechanical properties of an aerogel, which will be beneficial for space habitats.
Regolith
Scientists are thinking of a range of ways to turn the red dirt of Mars into building materials for habitats. One of the possibilities involves sintering regolith to produce bricks, which would then be assembled into a building. These blocks could provide protection against galactic cosmic rays and solar particle events, while also providing a good amount of thermal insulation.
However, this approach would require a lot of energy, so it may not be practical in the long run. Another option is to use masonry, with blocks of sintered or melted regolith used to construct walls, floors and ceilings. But this requires more complicated engineering, since it is harder to control the thermal stresses that lead to cracking.
Other proposals involve eliminating the need for a binder altogether. For example, UCSD’s Qiao has shown that it is possible to make bricks out of regolith simulants simply by compressing the material rapidly. The soil contains iron oxide and oxyhydroxide particles that are easily cleaved by high pressures.
Besides being a good shield against radiation, regolith is very tough and durable. So it would be ideal for paving lunar rocket launch sites and building debris shields surrounding landing pads. These barriers could even be constructed before humans land, giving the colonists a basic pressurized shelter to live in until they can move into their new home.
Concrete
Concrete is one of the most versatile building materials in construction. It can be used for floors, walls and roofs of buildings and is often paired with fireproof insulating foam to form a solid and durable insulated concrete block (ICF). Concrete structures are more resistant to forces like high winds and hurricanes than steel-framed buildings, but they also have higher lateral stiffness than other materials that allow them to move minimally in these conditions.
Researchers are exploring concrete as a building material for space habitats because it is structurally sound and offers radiation shielding properties, which will protect astronauts from harmful solar radiation and cosmic rays. Its thermal regulation properties are also useful, since it can help regulate temperatures in space.
To create concrete in space, a mixture of aggregates (like rock and gravel) and cement must be combined, but transporting these materials from Earth could prove to be expensive and time consuming. Scientists from the University of Manchester in the U.K., however, have found a solution. They incorporated a protein from human blood, urine, sweat and tears into a glue-like substance that holds together the aggregates of lunar or Martian dust to create a type of space concrete they call AstroCrete. The result is a hard material they say is 300 percent stronger than ordinary concrete.
Shape Memory Alloys
Shape memory alloys are metals that re-form to their original shapes after being deformed. They can do this when heated or subjected to stress. These adaptive materials are especially useful for creating expandable habitats and deploying solar arrays in space. They can also provide resistance to damage from radiation or micrometeorites.
The alloys use a process called reversible phase transformation to regain their shape. This involves atomic-level rearrangements, similar to liquid water to solid ice. The shape-memory alloys are reversible, which means they can be formulated to remember a specific shape.
Currently popular shape-memory alloys include NiTi (Nickel Titanium), CuZnAl, and CuAlNi. When a mechanical load is applied, the shape-memory alloy twizzles into a twinned state of martensite. When the load is removed, the material reverts to its austenite form at a temperature known as the transition temperature. At the transition temperature, the alloy is capable of undergoing the phase transformation back into martensite without reheating. This is what gives the material its pseudo-elasticity and shape memory effect.
Sandia is a member of the Consortium for the Advancement of Shape Memory Alloy Research and Technology (CASMART). The organization brings together government, academic and industry experts to share applied research on the alloys. Using this shared knowledge, the group is exploring potential applications for the alloys in wind and solar energy, as well as in satellites.