What could vegetables offer space exploration? According to the European Space Agency, a lot.
Last year, the agency unveiled the results of a collaboration with the Côte D’Azur University: a new, fully biobased epoxy resin composite.
The project shows how biomaterials can offer powerful functionalities in space travel with fewer health and environmental risks than petrochemicals.
Here is how biobased materials could support safer, more sustainable space travel.
Orbiting orange peels
The space-ready biobased resin developed by ESA and Côte D’Azur University was made from sawdust, fruit and vegetable peel, and brown algae. The project turned these into building block molecules that can form ultra-strong materials.
The team behind the Côte D’Azur-European Space Agency partnership believe that biobased materials like this could one day replace many petroleum-based materials in spacecraft.
Projects like this reflect growing concerns around the sustainability of the aerospace industry. The amount of space debris in orbit is increasing, with more than 25, 000 particles larger than 10 cm circulating around Earth alone, according to NASA.
There are also calls for space research to deliver innovations that solve problems back on Earth, such as pollution and climate change.
As well as meeting the challenges of space travel, the new biomaterials coming out of aerospace research could eventually help other industries decarbonise.
Circular, not just biobased
To maximise sustainability in spacecraft, using biological raw materials is not enough. Materials must also meet two more criteria: that they come from waste raw materials and they are recyclable.
The European Space Agency has followed both of these principles in designing its biobased resin. It has used waste matter, not crops, for building its space composites.
Waste feedstock cuts a biomaterial’s environmental impacts. Unlike crops grown for the purpose of building industrial materials, ordinary waste is already abundant and does not require water, land, and fertiliser to grow.
The European Space Agency has also formulated its biobased resin to be recyclable using non-toxic chemicals.
Recyclability is also a key consideration in cutting the environmental impacts embedded in space materials. Whether a biobased material is more sustainable overall than a petrochemical product can hinge on whether it can be broken down and used in new ways.
Sustainability is not the only driving force behind this research. Human health is another factor.
Most epoxy resins and thermosets are still made from petroleum. These contain hormone-disrupting bisphenol A and epichlorohydrin. Much of the motivation around developing the biobased resin came from the aim of reducing dangerous chemicals in spacecraft.
The biobased resin has gone through testing at the European Space Agency’s Research and Technology Centre in the Netherlands, where a 2, 500-strong technical workforce subject new technologies to the simulated rigours of space.
So far, production has only amounted to a few kilos of the biobased resin. The next step for the team is to scale and commercialise.
Taking the heat
Materials made from renewable feedstock can often offer functionalities for aerospace applications that are difficult to achieve using purely synthetic substances.
In the US, this is being proved through the long-term collaboration between private company Cambium and the US naval Air Warfare Centre.
The partners have developed a biomaterial that meets the need for less toxic fire-resistant materials in air and spacecraft.
Safe space travel relies on reliable fire resistance built into the construction of the craft. Fires are impossible in the outer vacuum of space but combustion inside the vehicle remains a risk. This is due to the presence of electrical systems and a lack of natural ventilation.
In 2020, the partners unveiled a composite biomaterial. It included molecules obtainable from plants and other biological sources, or produced from sugar via fermentation processes.
Health concerns drove the R&D. Many fire-resistant coatings in space and aircraft are based on halogen. These release highly toxic smoke while they burn. Cambium embarked on a search to find less toxic materials for the exterior and interior that still offer the same level of fire resistance.
Bamboo-aided spaceflight
The biomaterial developed by the European Space Agency is a polymer – a type of material composed of long molecular chains. Plastics are a kind of polymer, with most made from petroleum.
Biobased polymers are a convenient way to incorporate renewable materials into design, since industry is already familiar with oil-based polymers and their range of useful properties.
Yet space applications can draw on a much wider range of biomaterials than just polymers. Bamboo wood is one of them.
The wood of the bamboo has a strength-to-weight ratio that is approximately six times greater than that of steel. This means that it is both incredibly light and incredibly strong.
The unique combination of lightness, strength, and sustainability have already sparked research around the world into bamboo composites for a myriad industry applications.
In the aerospace industry, bamboo-based biomaterials could replace or supplement fiberglass, a material popular in making the bodies of aircraft and spacecraft.
Manufacturing fibreglass can release a lot of greenhouse gases because high temperature furnaces are needed in the process. Cutting the amount of fibreglass required with bamboo composites could lower the emissions associated with aerospace construction.
Bamboo’s combination of lightness and strength is attractive in aerospace because the weight of the craft is a huge determinant of project costs. Heavier crafts rip through fuel faster during take-off, racking up the price of launch.
Bamboo’s strength comes from its microscopic structure. The wood is composed of many tiny tubular bundles surrounded by supporting fibres. Within these supporting fibres are microfibres arranged in a highly ordered pattern. These structural arrangements make the overall material capable of absorbing large amounts of energy.
From a sustainability perspective, bamboo is difficult to beat. Compared to fibreglass the material takes far less carbon dioxide to manufacture. It is also biodegradable.
Bamboo biomaterials are not just one thing – the wood can be processed in many ways.
This could mean mixing bamboo fibres with other materials to form a bamboo-based composite. Graphene nanomaterials could be incorporated for added strength, for example. Infusing the cell walls of the wood with resin is another way of refining the natural material for specific applications.
Silken space spools
Another material found in nature that can surpass steel on strength and lightness is spider silk. The material is also elastic, capable of forming structures that stretch without breaking.
These properties make spider silk ideal for building more sustainable and less polluting spacecraft, as an additive in composite materials for on-board equipment or structural elements of the craft, as a sustainable and lightweight storage and packaging material, and for parachutes or ropes. Its elasticity also makes it ideal for patching up damaged equipment.
Sider silk in aerospace is still an emerging area of research. However, there are promising indicators that the material can be incorporated into spacecraft in different ways.
In 2022, a journal article published in Acta Astronautica revealed scientists reported on how a spider silk aircraft windowpane performed just as well as the current industry standard despite being lighter.
NASA is going a step further, looking into the possibility of spider silk production during actual space missions.
In 2019, the space agency announced research into equipping spacecraft with fermentation equipment. These would allow astronauts to manufacture spider silk compounds using specially engineered microbes. Astronauts could process these compounds into useful silk-based materials, like surgical sutures or fabrics, once landed.
Biomanufacturing equipment like this can extend the length of a voyage and cut costs by reducing unnecessary supplies on the outgoing flight.
Bio-inspired hygiene
On-board hygiene is another area where biomaterials can serve safer space travel.
In space, crew members travel light, dispensing with amenities we take for granted like water and detergent for laundry.
Without running water and cleaning supplies, maintaining hygiene is harder. Certain biomaterials with inbuilt microbial resistance could help.
Traditionally, anti-bacterial minerals like selenium, silver, and quaternary ammonium compounds have been applied as disinfectants on board spacecraft.
However, mineral-based anti-microbials like this pose a toxicity risk. There can be a thin line between the amount that kills bacteria and the amount that can harm human cells. In the closed confines of a spacecraft, the risk of these substances accumulating into harmful levels is higher.
Once again, the European Space Agency is leading research into incorporating biobased anti-bacterial coatings for space, investigating chitosan and lignin for their potential.
Chitosan is a compound found in crustacea while lignin is a natural polymer found inside most plant
Working with the Luxembourg Institute of Science and Technology, the agency found that lignin was a particularly effective additive for anti-bacterial solvents.
Another area that the agency is investigating is ‘nano-patterning’. Cicadas and dragonfly wings come naturally armed with tiny structures that physically kill bacteria that land on them. Man-made materials that imitate this using densely packed nano-sized ‘teeth’ can mechanically kill bacteria that come into contact with the surface.
These anti-bacterial nano-structures could be applied to textiles used for clothing, as well as for making anti-bacterial dressings.
The biomaterial innovations coming out of the aerospace industry prove how renewable, sustainable materials can excel in high performance applications while supporting human health and sustainability. For advanced biomaterials, the sky is the limit.
