On the afternoon of December 11, 1972, the Apollo 17 lunar module touched down in the Taurus-Littrow valley on the surface of the Moon. Over the course of the next three days, astronauts Eugene Cernan and Harrison Schmitt conducted three moonwalks, each more than seven hours long, collecting samples, taking readings, and performing experiments. In between, they returned to the lunar module, their home base. The mission, the last of the Apollo series, set a number of records, including longest total time spent on moonwalks and the longest time spent on the Moon.
To more fully explore celestial bodies like the moon and other planets, we’ll need to stay for longer than three days. And that means building some kind of long-term habitat for the people that make the trip. It’s a challenge that NASA engineers have long pondered, and one they aimed to solve by finding a way to construct that habitat before people arrive.
NASA’s 3D-Printed Habitat Challenge, a competition that began in 2016, asked teams from industry and academia to design not just a structure, but a complete system for autonomous extraterrestrial building—specifically for Mars, the closest habitable planet to Earth. The competition was divided into multiple phases, the first focused solely on design, the second focused on fabricating structural components, and the third, completed in 2019, focused on autonomous construction of a one-third scale model.
Each system was required to:
be autonomous, meaning that it could complete its function without direct human guidance. It had to be able to not only do the work, but evaluate the work, stay aware of changing surroundings, and adjust its plan to accommodate dynamic conditions. In other words, it had to know its goal but adapt to meet it in a flexible way without human interaction.
use materials found on-site for construction, what’s known as in-situ resource utilization (ISRU). The cost to transport one kilo of material to the Moon is approximately $12 million—even more to Mars—so shipping materials from Earth simply isn’t feasible. Instead, teams needed to find ways to build using the high-basalt soil and other materials found on Mars.
use off-grid power sources, meaning primarily solar and geothermal options, since sourcing fuel from Earth is not readily viable.
Multiple teams from the competition have led sessions at Autodesk University:
In the end, AI SpaceFactory took top honors in Phase 3 of the competition, with Penn State the runner-up. Ultimately, the competition was less about winning and more about driving innovation. And those innovations can be applied not only to how we build on other planets, but also to how we build on Earth.
“Off-grid power generation would mean lower energy use,” Bentley explained. “Autonomous construction would mean less waste on the job site. And in-situ resource utilization would mean we won’t have to rely on heavily polluting industries like concrete and steel.”
Michael Bentley of AI SpaceFactory presents in the AU Theater on the 3D-printed habitat that won NASA’s 3D-Printed Habitat Challenge.
The Need for Sustainable Construction
Earth’s population is 7.8 billion today—and it’s expected to near 10 billion by 2050. The McKinsey Global Institute estimates that, by 2025, 1.6 billion people living in cities will struggle to find adequate housing. To meet demand, some experts estimate we’ll need to build as many houses in the next 20 years as we did in the previous 2,000.
The problem? Construction is currently responsible for 11% of global greenhouse gas emissions, according to Architecture 2030. The production of one ton of Portland cement, the most common kind in use today, generates half a ton of carbon dioxide (C02), a leading greenhouse gas. And experts estimate that construction is responsible for 30% or more of the materials in landfills.
Simply scaling up production with current processes will also scale up waste and emissions just when we’re trying to reduce them. We need to find new ways to build that don’t harm our environment and the communities that live here. We can look to the NASA competition for innovative ideas on how to build more sustainably.
Bringing Learning Back to Earth
Each team in the competition developed their own approach to solving the challenges of autonomous building, combining hardware, software, sensors, AI, and locally-sourced materials. Instead of using concrete, three of the teams that led sessions at AU used plastic that can be recycled from landfills: NASA Swamp Works, for example, chose PETG, the kind most commonly used for water bottles.
Jacobs is a global engineering and construction services firm that has provided engineering support for NASA’s Marshall Space Flight Center for decades. In his AU Theater talk, Kurt Maldovan, a digital engineering lead at Jacobs, shared how the automated additive system they developed for this NASA challenge is “safer, produces less waste, and requires less personnel” than traditional building processes. Additive techniques by definition reduce construction waste by 60-90%, according to Maldovan, and they can compress build schedules by 80%, from five days to one.
The system they developed, which they call Automated Construction of Expeditionary Structures (ACES), while not fully autonomous, prints at a rate of 500 inches per minute and reduces the need for construction materials by half, from 5 tons to 2.5 tons. A related system developed with several branches of the U.S. military enables rapid deployment teams of only four people to put up a 500-square-foot structure in 40 hours; with previous systems, teams of ten needed five days. The same system could also play an important role in disaster relief.
It may be the lessons about sustainability that provide the most value in terms of transforming construction. The winning system from AI SpaceFactory 3D prints a cylindrical structure called MARSHA (short for Mars Habitat) made from a combination of crushed basalt regolith and PLA plastic, a biopolymer that can be made from corn or sugar cane. This makes it “both recyclable and compostable,” according to Bentley. “So as soon as MARSHA came down, we decided to grind it up and reprint it near New York City as TERA—MARSHA’s earthly cousin.”
The terrestrial version is extremely energy efficient—it took only 7,200 kilowatt-hours to build. Growing the plants for the PLA material sequesters 8.5 tons of carbon from the environment. Using PLA made from recycled sources uses 7,500 pounds of plastic waste.
Bentley calls this “a new approach to building and construction that is cradle-to-cradle. You can grow this material, print habitats with it, recycle it a number of times, and then eventually put the material in an industrial composter and return it to be bio-mass.” He calls it “a new way of building on planet Earth.”
To Mars and Back
On December 14, 1972 astronauts Cernan and Schmitt lifted off from the lunar surface and rejoined the Apollo 17 spacecraft in orbit. Four days later, they were back on Earth. The mission was a success, the culmination of the many scientific and engineering achievements of the Apollo space program. It was also the last time a human set foot on the Moon—or any planet besides Earth, for that matter.
NASA’s Artemis program aims to return people to the Moon by 2024. From there, NASA scientists are working on programs that will get us to Mars, where rovers are already mapping the planet. These missions can tell us more about our solar system, our universe, and the possibilities for life on other planets. The systems developed during the NASA 3D-Printed Habitat Challenge go a long way toward making that possibility a reality.
But a manned mission to Mars is decades away at best. Until then, our focus remains on what happens on Earth. The approaches and processes adopted by the NASA challenge competitors may not be those you’ll adopt on your next construction project, but autonomous construction technologies are coming to market, from quadruped robots that can navigate dynamic construction sites to perform tasks such as laser scanning to autonomous robots that can print wall layouts on concrete slabs from BIM models. In the years and decades to come, these innovations and others like them may become important tactics to meet growing global demand more quickly with less negative impact.
“Additive manufacturing technology has the potential to revolutionize the way we do construction here on Earth,” says Massimiliano Moruzzi, an Autodesk senior research scientist who worked on the NASA Swamp Works system. “If we can repurpose plastic pollution and use readily available natural resources to robotically print houses on other planets, we can use the same approach to sustainably build streets, sidewalks, playgrounds, and even structures here at home.”
Michael Bentley sees the results of the NASA competition as perhaps a turning point. “We weren’t able to go to space,” he said of his team and their design. “But we were able to think very carefully about what it means to build on another planet in that kind of extreme environment. And we realized that the lessons that we learned hacking those challenges could be helpful for how we build in a more sustainable and responsible way here on Earth.”