Now that NASA and SpaceX have set their sights on Mars as the next destination for human exploration, one of the most pressing problems is how astronauts will go about living on the Red Planet once they get there. To this end, researchers around the globe are working on everything from space farming to the interplanetary internet, but some of the most exciting developments are happening in Martian home design.
So far, all the ideas for Martian habitats have been pretty unremarkable, generally adopting some variation of the 'tin can' or 'bounce house' design. But a recent wave of innovation has opened up the possibility of Martian houses that are made from far more exotic and easily sourced materials, such as 3D printed bricks of ice, compressed Martian regolith, microbial cement, and even mushrooms.
Most recently, a team of materials scientists based at UC San Diego forged bricks out of JSC Mars-1a soil, a popular simulation of Martian regolith with approximately the same chemical composition found on the Red Planet.
The work represents a key step toward "Martian masonry," in which habitats are crafted from onsite resources, which would save future missions the cost and space of schlepping Earth materials to another planet. At the moment, only small regolith bricks have been created in USCD's laboratory, but the long-term goal is to manufacture bricks with practical sizes and applications.
"Our current work is focused inch-sized small samples, for materials study," study author Yu Qiao told me over email. "Scaling up to the structural level will be the next step."
Qiao and his colleagues created their samples by compressing Mars-1a soil at ambient temperatures, without treating the material with any additives. They found that nanoparticulate iron oxides and oxyhydroxides (npOx), the elements in Martian regolith that give the soil its reddish hue, also act as powerful bonding agents. When compacted, the oven-dried simulant had "flexural strengths exceeding that of typical steel-reinforced concrete," according to the paper.
While you are free to start scouting out Google Mars for a good spot to build your Martian hacienda, Qiao and his colleagues need more lead time to devise the best method for manufacturing bricks and cinderblocks on another world. "There are various directions that we'd like to study to make large parts, from drop towers (like a piling system) to soil compaction system," Qiao told me, "but we have not had time to do the work yet."
In the meantime, Lynn Rothschild, an astrobiologist at NASA's Ames Research Center, is working on figuring out how to build Martian mansions from microbes and synthetic biomaterials.
During her presentation at the recent Astrobiology Science Conference in Phoenix, Arizona, Rothschild encouraged the assembled astrobiologists to think of "biology as technology" when it comes to designing blueprints for the Red Planet. For example, Rothschild cited microbial calcite precipitation, which is basically a fancy way of describing a technique for using microbes to create a binding agent that could turn Martian regolith into a natural cement.
Astronauts could take a leak on a mixture of microbes and Martian regolith to make cement
This approach to architecture has already been well-tested on Earth, and according to Rothschild, the microbes involved could be bioengineered in order to do their thing in the harsh Martian environment. Moreover, it is possible to facilitate this process using microbes that live on urea, an organic compound found in urine, meaning that astronauts could take a leak on a mixture of microbes and Martian regolith to make cement. But according to Rothschild, in the Martian economy, urine has far more valuable uses than just making bricks.
"It's a waste of pee," she said with a laugh. "I can't believe I just said that."
If microbial masons aren't your thing, Rothschild is also exploring how 3D printing biomaterials could literally lay the foundations for future Martian homesteaders. For example, she considered how bioprinting could would be used to artificially recreate bone, which Rothschild considers to be an ideal for homebuilding due to its inherent strength, limited flexibility, and ability to restructure.
Both of these biological approaches to construction are pretty wild, but they don't hold a candle mycotecture, a way of building houses out of the root-like structure of mushrooms called mycelium. This would work by essentially taking some mushroom spores, putting them in a container that is the desired shape, and then adding some water and a growth medium such as sawdust or flour. Within days, this mixture will have created a building material that is as durable as a piece of plywood, in the shape of the original container.
Mycotecture has a number of advantages over the other approaches to Martian architecture, particularly when it comes to its ability to grow incredibly quickly, take any shape, and self-repair. Rothschild imagines a scenario in which future Martians overlay a skeleton structure with a double-layered plastic bag which is used to grow mycelium—kind of like pitching a mushroom tent.
Moreover, any damage to this structure could be easily repaired by growing more mycelium. And if the Martians really wanted to get fancy, they could genetically engineer the mycelium using colored proteins that are attached to genetic markers so that the cell changes color when that gene with the attached protein is activated (a common lab technique called reporting).
If that gene in the mycelium becomes activated in response to drops in pressure, the walls of a Martian myco-home would change colors when the pressure in the structure dropped, warning the Martians that repairs were needed and ideally preventing suffocation.
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When I spoke with Rothschild at the conference, her excitement about mycotecture was palpable. She gained notoriety a few years ago for a biodegradable drone (also made from mycelium) that she and her colleagues had developed as a tool for exploring Mars. By applying these techniques to Martian living, she hopes to overcome the biggest challenge facing interplanetary travel: the "mass problem" that results from having to schlep so much stuff from Earth to the Red Planet.
"Brick, printing ice, mycotecture, they're not mutually exclusive," Rothschild told me. "Let's get creative and think about biology as technology, rather than something that technology has to be applied to."
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