NASA and the China National Space Agency (CNSA) plan to mount the first crewed missions to Mars in the next decade. These will commence with a crew launching in 2033, with follow-up missions launching every 26 months to coincide with Mars and Earth being at the closest point in their orbits. These missions will culminate with the creation of outposts that future astronauts will use, possibly leading to permanent habitats. In recent decades, NASA has conducted design studies and competitions (like the 3D-Printed Habitat Challenge) to investigate possible designs and construction methods.
For instance, in the Mars Design Reference Architecture 5.0, NASA describes a “commuter” architecture based on a “centrally located, monolithic habitat” of lightweight inflatable habitats. However, a new proposal envisions the creation of a base using organisms that extract metals from sand and rock (a process known as biomineralization). Rather than hauling construction materials or prefabricated modules aboard a spaceship, astronauts bound for Mars could bring synthetic bacteria cultures that would allow them to grow their habitats from the Red Planet itself.
The concept, known as “Biomineralization-Enabled Self-Growing Building Blocks for Habitat Outfitting on Mars,” was proposed by Congrui Grace Jin, Ph.D. — an assistant professor of civil and environmental engineering at the University of Nebraska, Lincoln. Her proposal was one of several selected by the NASA Innovative Advanced Concepts (NIAC) for Phase I development, which includes a grant of $12,500. This program makes annual solicitations for advanced, innovative, and technically feasible concepts that assist NASA missions and further the agency’s space exploration objectives.
Since the 1990s, several architectures have been drafted for crewed missions to Mars, all of which have emphasized the need for keeping launch mass low. Suggestions for how this could be accomplished include inflatable modules. But as Jin emphasized in her proposal, the physical structures used to outfit the inflatable modules cannot be carried by a crewed spacecraft and generally require a second vehicle to launch them. This is a logistical challenge for missions and drastically increases launch costs.
Another possibility is to use local resources to reduce the number of supplies that must be transported — a process known as In-Situ Resource Utilization (ISRU). Examples range from the Mars Direct proposal drafted in 1991 by Robert Zubrin, Ph.D., and colleagues from NASA’s Ames Research Center to NASA’s Journey to Mars program launched in 2010. For missions to Mars, this would include using local regolith to create building materials and water ice for astronaut consumption, irrigation, and to create propellant and oxygen gas.
However, this mission architecture requires equipment (like robotic 3D printers) to be transported to Mars. In addition, many designs for ISRU-3D printed habitats still require inflatable modules, which provide scaffolding for 3D-printed structures. For her proposal, Jin suggests that rather than shipping prefabricated elements or machinery to Mars, habitats could be realized through in-situ construction using cyanobacteria and fungi as building agents.
Via Zoom, Universe Today recently interviewed Jin, who explained the road that led to her NIAC proposal: “In the past few years, I have been working on self-healing concrete. So when concrete generates cracks, we use bacteria or fungi to induce the biominerals to heal the cracks. And then we think about other possibilities, like self-growing materials. So one would have soil particles or aggregates. We want to use fungi or bacteria to make them into a cohesive body.
“This will be very important if there is no human labor, especially on Mars. They can do this automatically. We propose that instead of shipping materials from Earth to Mars, we can directly use in-situ materials. For sample, the soil, the atmosphere, and the water on Mars, then we can just bring some bacteria or fungal spores, and they will build the bricks for us.”
The key to this is “biomineralization,” a process in which bacteria and spores can assemble minerals like calcium carbonate (CaCO3), otherwise known as limestone. Scientists have known that there is limestone and other carbonates on Mars, as demonstrated by the Pheonix Mars Lander that found traces of CaCO3 at its landing site in 2008. This was backed up by subsequent sample analysis conducted by the Spirit and Opportunity rovers and mineral mapping conducted by missions like NASA’s Mars Reconnaissance Orbiter (MRO).
According to Jin’s proposal, future missions could be equipped with “synthetic biology toolkits” to create synthetic lichen systems (diazotrophic cyanobacteria and filamentous fungi). These will turn CaO3 into abundant biopolymers that can be combined with Martian regolith to “grow” building materials. “They will work as a catalyst to promote the calcium carbonate formation, and those calcium carbonate crystals will work as a glue to bind those soil particles together,” said Jin. “You need to put the sand particles into the mold you want, then the bacteria and the fungi will grow them into the shape of the mold.”
In this proposed autonomous system, the cyanobacteria and filamentous fungi perform different but complementary functions. As per the NIAC proposal, the cyanobacteria are responsible for 1) capturing carbon dioxide and converting it to carbonate ions and 2) providing oxygen and organic compounds to support the filamentous fungi. The fungi, meanwhile, are responsible for 1) binding calcium ions onto fungal cell walls and serving as nucleation sites for calcium carbonate deposition and 2) assisting the survival and growth of cyanobacteria by providing them additional carbon dioxide and reducing their oxidative stress.
In addition, the cyanobacteria and fungi secrete “extracellular polymeric substances” that enhance adhesion between regolith particles and biopolymers and cohesion among precipitated particles. Dr. Jin also detailed the process for creating these synthetic bacteria and fungi, which ensures that they work symbiotically and not competitively:
“We need to find those strains that can get along with each other. It’s called mutualistic co-culturing. Basically, some of them can enhance the living of the partner. We need filamentous fungi because of their filamentous structure. They can promote larger amounts of calcium carbonate crystals. But we also need the cyanobacteria can do photosynthesis — they can capture the CO2 and generate organic carbon for the fungi.”
To get this process started, there is still equipment that will need to be brought to Mars. Due to the low-pressure atmosphere, radiation, and temperature extremes, Jin says that future missions will need to bring a photobioreactor. This bioreactor is where the cultures of bacteria and lichens will grow and where the assembly process will occur. Ultimately, the proposal envisions bioreactors producing bricks that are removed to build surface structures. As for the rate of production, Jin contends that more research is needed: “It really depends on the nutrients, the temperature, and the pressure. So we are still studying this process. We want to optimize the factors that influence the process so that we can do this much faster,” she said. However, another benefit is how these building materials will also be self-healing. “If you don’t kill the bacteria or fungi, they can always generate those limestone crystals. So later, when the structure generates cracks, they can heal them automatically. So this material is self-growing and self-repairing. So they have a lot of features that we don’t have with materials on Earth.”
While biomineralization is something researchers have been investigating for years, this proposal represents a first for two reasons. For starters, it is the first project to consider filamentous fungi as a biomineral producer instead of bacteria. Jin has conducted extensive research on biomineralization in recent years, and her results have demonstrated that filamentous fungi possess distinct advantages over bacteria. Foremost among them is their extraordinary capacity to produce large amounts of minerals in a short space of time.
Second, this project is the first to employ self-growing technology by creating a synthetic lichen system and using symbiotic interactions between photoautotrophic cyanobacteria and heterotrophic filamentous fungi. Photoautotrophs are noted for using sunlight to turn inorganic carbon into organic materials (in this case, organic carbon). None of the self-growing practices investigated so far have been fully autonomous since they were generally restricted to a single species or strain of heterotrophs dependent on a constant external supply of organic carbon.
This technology has applications beyond space exploration as well. Aside from building habitats on Mars and other bodies beyond Earth, the technology also has the potential to revolutionize construction here on Earth. In regions that have been affected by war, natural disasters, and climate change, this autonomous, self-growing technology has the potential of “healing” damaged structures and building new infrastructure in a way that has a negative carbon footprint. Since the process relies on CO2 captured from the atmosphere, it is consistent with global climate restoration efforts.
This technology is yet another example of how Earth organisms and biological processes inspire sustainable and regenerative space systems. These same technologies, which could allow humanity to live sustainably in space, could also help us combat and reverse climate change here at home. Much like the process that powers this proposed bioreactor technology, the relationship is symbiotic.