How to build your Martian dream house
Some day, humans will live on Mars. That’s the vision of some of today’s highest-profile forward-thinkers. This week, in an op-ed for CNN, President Barack Obama wrote that he hopes America will send humans safely to Mars and back by the 2030s. And late last month, SpaceX founder Elon Musk announced plans to colonize Mars within the next 50 to 100 years, with the help of the most powerful rocket ever, sending up a reusable spaceship that could carry a hundred humans at a time to the Red Planet.
But once the expat Earthlings land, what kind of structures will they live in? Scientists are working on myriad answers to that question (among others). One major obstacle to homebuilding on Mars is the limited capacity of any realistic spacecraft to carry all the materials needed to erect substantial, durable habitats. Ideally, the pioneers would use local materials, just as early European settlers in North America chopped down pines to build log cabins. With no forests on Mars, what can 21st-century space settlers use?
There is water on Mars—most of it frozen. That’s one of the attractions that make the fourth rock from the sun a good candidate for colonization. (It also has an atmosphere to absorb radiation, a surface temperature range that could be bearable with the right protective gear, and a day/night cycle similar to ours at 24 hours, 37 minutes.)
So when NASA held its 3D-Printed Habitat Challenge last fall, one team of designers tapped H20 as its substance of choice to fabricate homes. Team Space Exploration Architecture (SEArch) and Clouds AO topped 165 entrants with their design, Ice House. The design takes a page from Alaska’s Inuit people, who for centuries have built temporary shelters out of snow during hunting expeditions. Envisioning a settlement in Mars’ northern climes, the NASA competition winners proposed that frozen water be harvested from the subsurface and run through a massive 3D printer to craft a sleek shell of ice that would cover the astronauts’ lander (which would serve as the living quarters), sealing it in a pressurized, habitable environment. Then another, still larger ice shell would be created to cover the first, not unlike a Russian nesting doll.
The multi-layered setup is designed for redundancy—you’d probably feel safer with a backup shell, wouldn’t you?—but the general purpose of the ice shell is to give the colonists a kind of artificial yard: they could obtain a feeling of being outdoors without having to suit up and venture out into the planet’s harsh environment. That’s because the translucent outer ice shell, while repelling cosmic rays, would let in sunlight, something vital to the colonists’ food garden, not to mention their sanity. And with temps in the region (Alba Mons) consistently below freezing, the shell would stand year-round without melting.
But what if the explorers wanted to conserve that water for other uses, like drinking it?
Smells like solid construction
Researchers at Northwestern University point to another material readily available on Mars: sulfur, which could be used to make sulfur concrete. NASA actually looked into lunar sulfur concrete in the 1970s, but with no atmosphere on the moon, the material would simply turn to vapor. Since that time, engineers have experimented with sulfur concrete applications right here on Earth, especially in underwater sewer pipes and artificial coral reefs. (The material is highly resistant to corrosion, but not fire.)
But when they mixed sulfur with Martian soil, the Northwestern scientists got some surprising results. Conventional concrete is made of water mixed with cement and gravel; sulfur concrete is simply sulfur and aggregate (sand and rocks). For their aggregate, Associate Professor of Civil and Environmental Engineering Gianluca Cusatis and collaborators substituted the Martian variety. “We bought a bag of Martian soil on the internet,” Cusatis said by phone with a laugh. “Of course, it’s a simulant, recreated with chemistry,” based on the real samples collected and analyzed by NASA’s Curiosity rover. As for sulfur, the element, it’s found in deposits on both planets.
In several experiments, detailed in their study in Construction and Building Materials, Cusatis’ team mixed the soil and sulfur in different proportions, eventually arriving at 50/50 as the optimal mix. After stress-testing cylinders of the end product, they found that it was twice as strong as sulfur concrete made with lunar aggregate. Indeed, with a compressive strength of about 8,000 pounds per square inch (PSI), the Martian concrete holds its own against typical Earth concrete, which runs between 3,000 and 6,000 PSI. And if it’s used on Mars, that 8,000 figure triples—to 24,000 PSI—owing to the planet’s lower gravity.
“We need to do more experiments, but we believe the Martian soil is not inert, but actually reacts chemically with the sulfur,” to produce the stronger blend, “and that is not the case with lunar soil or with the sulfur concrete here on Earth,” Cusatis said.
Theoretically, NASA or SpaceX or another entity could send expeditions of robots to mine for the sulfur, mix the concrete, and perhaps even construct the buildings, again with 3D printing technology. Like any of the proposed Mars missions, it would take years and cost billions to pull all this off, but sulfur concrete might save some time and money. It requires less energy to heat (248 degrees Fahrenheit, versus 2,550 for standard concrete), and only takes an hour to cool and harden (versus days for the standard stuff).
Cusatis doesn’t claim the material is perfect, especially not at this early stage of the research. Some kind of liner might have to be developed to mask the rotten-egg smell of the sulfur. And as noted above, sulfur concrete is not terribly resistant to high temperatures, so until the material can be engineered to be fireproof, settlers would have to be careful about cooking. Then again, the early English settlers in the New World built thatch-roofed houses that wouldn’t pass inspection today; sure enough, those structures burned or tumbled down, but in the long run that didn’t stop the colonies from taking root. In the same way, Cusatis believes sulfur-concrete homes might provide adequate shelter for the first generation of pioneers on the Red Planet.
What about a (relatively) quick way to plop down finished houses on Mars’ surface, without going to all the trouble of mining for ice, sulfur, or anything else? With a great deal of publicity in 2012, the Dutch company Mars One announced a plan of Icarian ambition to plant a permanent colony on Mars by 2024. A team of MIT students picked apart the plan and deemed it unrealistic last year.
But at least one element of Mars One’s vision is rooted in reality. The technology for its imagined Living Units is based on that developed for NASA by Bigelow Aerospace, and in use right now: an inflatable habitat. The experimental Bigelow Expandable Activity Module (BEAM) docked at the International Space Station last April. (The company prefers “expandable” to “inflatable,” perhaps because the latter evokes kids’ bouncy houses, or because BIAM is an inferior acronym.) There, astronauts are conducting habitability tests over a period of two years.
The advantage with BEAM is it takes up less room in transit. Made of a proprietary layering of “soft goods,” the structure’s skin is scrunched into a small package (5.7 feet long and 7.75 feet in diameter) for the space voyage. Then upon arrival, it’s inflated (or expanded) to its pressurized dimensions, 13 feet long and 10.5 feet in diameter.
If the experiment on the space station succeeds, it could translate into applications on Mars, whether by Mars One or another exploration project. Mars One envisions using Bigelow’s technology to send living units to the planet ahead of time. When settlers land, they can move right in. According to the company’s website, inhabitants will “be able to shower as normal, prepare fresh food (that they themselves grew and harvested) in the kitchen, wear regular clothes, and, in essence, lead typical day-to-day lives.”
Typical day-to-day lives? Maybe not quite. But whatever kind of domiciles the Martian colonists live in, they’ll be benefiting from the work of builders who thought way, way outside the box.
This post was written by Suffolk Construction’s Content Writer Patrick L. Kennedy. If you have questions, Patrick can be reached at PKennedy@suffolk.com. You can connect with him on LinkedIn here or follow him on Twitter at @PK_Build_Smart.