In a cavernous arena outside of Peoria, Illinois, two industrial robots worked against the clock last weekend to finish their tasks. Each had been converted into a towering 3-D printer and programmed to build one-third-scale models of extraterrestrial habitats. For 30 hours over three days, generators chugged and hydraulics hissed as robotic arms moved in patterns, stacking long beads of thick “ink” into layers. Gradually, familiar forms began to emerge from the facility’s dirt floor: a gray, igloo-like dwelling and a tall, maroon egg.
Humanity’s future on Mars was taking shape.
The machines belonged to two teams, one from Penn State and the other from a New York-based design agency called AI SpaceFactory, that were competing in the final phase of NASA’s 3D-Printed Habitat Challenge. Each team had to develop an autonomous printer that operated with as little human intervention as possible, used materials or recyclables found on Mars or the moon, and passed the scrutiny of judges as well as rigorous structural testing.
The stakes were high. The winner would take home US $500,000. Lessons the teams learned would inform not only how humans might one day survive on Mars, but also how they might live more sustainably on Earth.
Penn State (left) and AI Space Factory (right) worked against the clock to 3-D print two distinctly different habitats from completely different materials.Photo: Tracy Staedter
“It’s taking high risks that could potentially bring high paybacks,” said Monsi Roman, program director for NASA’s Centennial Challenges (of which the 3-D Habitats competition is one).
Manufacturing the two most common building materials, steel and cement, produce more than 15 percent of the world’s carbon emissions. And only about a third of a demolished building gets recycled, said AI SpaceFactory’s Founder and CEO David Malott, who worked as a skyscraper architect in New York City for 20 years. “I think we’ve already reached a tipping point where we’re building in an unsustainable way,” he said.
In the first hour of 30, AI SpaceFactory's 3-D printer began laying down the first of many layers of a recyclable composite made from basaltic fibers and a bioplastic derived from plant starch.Photo: NASA
To build their 15-by-8-foot egg-shaped structure called MARSHA (for Mars Habitat), Malott and his team used a recyclable composite made from basaltic fibers and a bioplastic derived from plant starch. Heated to about 350 degrees Fahrenheit before it’s extruded, the substance cools and sets in about 5 minutes into a strong, reusable material. “At the end of the building’s lifecycle, it can be recycled, or we can actually compost it,” he said. “You can imagine that you’re growing your next generation of buildings from the dirt.”
Penn State's 3-D printer extrudes a cement made from river sand that mimics rocky soil found on Mars.Photo: NASA
Penn State’s team used a river sand-based cement to build their structure, which they named PennState Den@Mars. The cement comes out wet and sets faster than conventional concrete, making it stronger more quickly, too. After 120 minutes, it won’t deform. When completed, the structure resembled two side-by-side igloos, each with a cone-shaped roof. Shadi Nazarian, associate professor of architecture and co-coordinator of the project with professors Jose Duarte and Sven Bilen, said they chose that shape to test how steep they could make the angle without using a mold. With each layer supporting the one above it, they were able to achieve two 12-by-7.5-foot structures with roof angles of 65 degrees.
“These are probably some of the largest 3D-printed structures printed in place in North America,” said civil engineer Peter Carrato, a fellow at the Bechtel Corporation and head judge for the competition.
Carrato oversaw 13 volunteer judges, all wearing bright yellow shirts, who awarded points for criteria such as the level of autonomy, the quality of the structure, how closely the materials represented those which could be found on Mars or the moon, and the structure’s durability and strength.
Both teams encountered several challenges as they raced to finish printing their structures in the time allowed. To start, the test facility, Caterpillar’s Edwards Demonstration and Learning Center, temporarily lost power on the first day, delaying operations.
When it came back on, the Penn State team realized that the conveyor belt that transported cement powder had reversed, causing the printer to extrude only water. It didn’t help that they had to start and stop the printing over a three-day period, either. That schedule introduced planes of weakness called cold joints, which occur when earlier layers of concrete set before new layers can intermix. At one point, Penn State had to change the printer’s nozzle head, which shifted the robot’s arm. When it began printing again, the beads were slightly off center and team members on the floor had to communicate instructions to a remote operator on how to reposition it.
As the AI SuperFactory group neared completion and the diameter of their structure narrowed near the top, they realized that the warm layers of composite had begun to slump together. They intervened to slow the robotic printer to a crawl to deposit more material and level out the print. Meanwhile, the clock counted down. In the final seconds, AI SuperFactory’s robot maneuvered to cap the structure with a skylight made from plexiglass and aluminum. But the opening was too wide, and the skylight fell through, hitting the dirt floor with a thud. For a moment, spectators looked around in confusion, but then burst into applause for both teams’ achievements.
A 26-pound weighted ball took a chunk off the Penn State habitat.Photo: NASA
But the competition wasn’t over. The fourth day began with several tests meant to push the habitats to the limit. The first involved blowing color-tinted smoke into the structures to reveal cracks or other flaws. Without their skylight, AI SuperFactory’s structure looked like a smokestack. Next, judges dropped three weighted balls—a 16-pound one, a 20-pound one, and a 26-pound one—from a height of 14.76 feet onto the structures. Penn State’s habitat survived the first two shots, but chipped on the third. Because AI SpaceFactory’s skylight had dropped inside and it had no roof, it didn’t undergo this test.
Lastly, the structures were subjected to a compression test. All personnel and a hundred or so members of the public moved into a theater that looked out onto the arena from behind safety glass. The crowd murmured with excitement as a 96-ton Caterpillar excavator with a 32-foot boom drove out onto the dirt floor.
Both structures underwent a compression test that subjected them to upwards of 50,000 pounds of force.Photos: NASA
Like a large hand pressing down on an egg, the excavator’s shovel compressed the top of AI SpaceFactory’s structure. It hardly budged. The machine’s treads began to rise off the ground. Only then did a chunk of material break from the structure’s top. The crowd cheered. Penn State’s structure showed resilience, also raising the excavator’s treads, but ultimately crumbled and received a round of congratulatory applause.
Specific details from the day’s testing, including the final scores, will not be released to the public, said Lex Akers, Dean of the Caterpillar College of Engineering and Technology at Bradley University, which partnered with NASA on the event. But when judges tallied the scores, AI SpaceFactory came out ahead, winning $500,000. Penn State received second place and $200,000.
Now, both teams are going back to the drawing board to refine their designs and ready themselves for a possible fourth phase of the competition, which Roman says has not yet been defined. In the meantime, AI SpaceFactory plans to recycle their structure, print a full-size Earth habitat named TERA (for Terrestrial Analog), and turn it into an Airbnb rental.
“This is a way to harvest buildings and return them to the earth,” said Malott.
Tracy Staedter is a science writer, editor, writing coach, and consultant. Over the 20-plus years of her career, she has covered a range of science and technology stories from astrophysics to zero waste. She worked on staff for such publications as Astronomy, Scientific American Explorations, MIT Technology Review, DNews, and Seeker. She also wrote the illustrated book, Rocks and Minerals (part of the Reader’s Digest Pathfinders series) and founded the Fresh Pond Writers workshop for fiction and creative nonfiction writers. In addition to contributing to IEEE Spectrum, she writes for Discover, Smithsonian Air & Space, Mercury Magazine, Inside Science, and more.