Creating sustainable extraterrestrial habitats will be an enormous challenge. Building materials that are durable, cost effective and able to resist radiation are crucial for the success of this endeavour.
The innovative sandwich material MAdFlex offers improved stiffness performances and enhanced folding behavior to simplify structural design of space habitats in deployable and foldable configurations. This is particularly important in space missions with limited storage and launch capacities.
Aerogels
Aerogels are a group of gel-like materials that have the remarkable ability to trap huge amounts of air within their structure. The result is that these materials can effectively insulate and are also capable of absorbing sound. They can also be transparent and can allow light to pass through them but block the transfer of heat, making them ideal for future space habitats.
The first aerogels were made by Stanford University’s S.S. Kistler, who used a unique technique to dry gels without collapsing the fragile network of molecules inside them. He replaced the liquid solvent with air and removed it using supercritical pressure to avoid boiling or liquefaction. The resulting aerogels were the first of their kind and are extremely light, strong and insulating.
A new method of making aerogels uses polymers to modify the surface, which makes them more robust and allows them to resist greater stresses before they start to deform or break. The process is known as ‘polymer reinforcement’. The result is that the new aerogels can be as stiff and durable as concrete but are 10 times lighter, with similar insulation properties.
Hybrid aerogels, which combine organic and inorganic components, have the potential to offer space missions sustainable insulating solutions by minimising the need to transport heavy insulators from Earth. By using local regolith, 3D printers can manufacture these insulators in situ, customised to the mission requirements and local environment.
Concrete
Concrete isn’t the first material that comes to mind when dreaming of space habitats, but this ubiquitous construction material could actually be ideal for outer-space living. Concrete provides resistance against the lethal radiation and micrometeorites that would quickly punch holes in regular structures, as well as thermal regulation properties that could help maintain comfortable temperatures.
It also doesn’t require any additional materials from Earth, since the sand, gravel and rocks that make up concrete are bound together by the cement powder that forms its matrix. Instead, researchers may be able to use aggregates found on Mars or the moon for this purpose.
In a recent study, Lepech and her team used potato starch to create a binding agent they called “bio-concrete.” When mixed with simulated extraterrestrial dust, the resulting StarCrete was twice as strong as normal concrete, which they say suggests it could be used for construction in space.
But for the real deal, it will need to be modified for the unique conditions of space. For example, the protein in human urine is an excellent binder for concrete, but it’s not practical to transport urine to Mars, and it might jeopardize astronaut health. To address these challenges, the research group is currently working on a version of StarCrete that uses common salt instead of urine. They’re also experimenting with a different binder, the organic polymer chitin, which is found in the exoskeletons of crustaceans and insects.
Shape Memory Alloys
Shape memory alloys, a group of metals that can revert to their original shapes when heated or triggered, are one type of material that could be used to build space habitats. The technology can provide adaptive capabilities in harsh environments such as the Moon and Mars.
Researchers have developed a model that predicts the internal temperature distribution of shape memory alloys during loading-unloading cycles, which can help to determine how much stress they experience. This is important for determining whether an SMA will fail due to mechanical damage. The researchers’ model uses a combination of thermodynamics and mechanical equations to assess the impact of the alloy’s environment, diameter and loading rate on its internal temperature.
This model can be used to optimize the performance of shape memory alloys for seismic applications, such as deploying or recovering buildings in an earthquake. It can also be used to develop and test new shape memory alloy compositions, such as copper-based and iron-based materials, for use in seismic applications.
SMAs are made of metals that have a special ability to recover from high strains by reversible phase transformation between austenite and martensite. This reversible phase change is triggered by heating of the alloy above its critical transition temperature, which can be determined using a thermal analysis technique such as differential scanning calorimetry (DSC). When a load is applied to an SMA above its austenite finish temperature, Af, but below its martensite deformation temperature, Md, the material will begin to exhibit elastic-plastic behavior. As the load is progressively removed, the alloy will revert to its original shape, with the detwinned martensite phase reversibly transforming back into austenite at its transformation temperature, Ms.
Regolith
The surface regolith of a space habitat offers an advantage over traditional construction materials in that it can protect astronauts from the radiation that bombards our planet. The surface material can absorb solar particle fluxes and provide a natural thermal insulation, preventing the surface temperature of a habitat from fluctuating widely with the sun’s activity. It also provides the opportunity to scavenge waste material for a variety of applications.
For example, a layer of 0.7 cm of regolith shielding can attenuate surface-to-space exposure (SPE) to less than a few mGy-Eq on average and significantly reduces the ionising dose for astronauts living inside the shelter. The thickness of the layer can be increased with plastic waste from the astronauts’ clothing and equipment, reducing the overall cost of the shielding to just over 1 USD per square metre.
In addition, sintering and casting methods can be used to turn loose regolith into building blocks for structures such as roads, berms to prevent dust accumulation during launches and landings, and even structural habitat elements. These processes require some form of thermal energy, such as passive solar, concentrated solar or microwaves, Farries told Lab Down Under.
In-situ resource utilization (ISRU) is a hot topic in construction on the Moon and Mars, where the environment is very different from Earth. However, AM technologies can be adapted to these conditions and offer the potential for prolonged off-Earth fabrications using local planetary materials.