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Researchers Take Steps Toward Lunar Construction
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A rendering of a robot, collecting lunar raw materials
University of Southern California researchers will spend the next two years trying to prove that lunar raw materials can be collected and mixed by robots to build infrastructure on the moon. Courtesy of NASA 

Engineers and architects at the University of Southern California are collaborating with NASA to develop and refine robotic construction technology that has the potential to transform the lunar surface with buildings and roads. 

September 11, 2012—Slightly more than 40 years after astronaut Neil Armstrong first stepped onto the moon’s barren surface, a team of engineers and architects at his alma mater, the University of Southern California (USC), are developing the technology to build infrastructure on the lunar surface. Led by Behrokh Khoshnevis, Ph.D., a professor of industrial and systems engineering, the team has been awarded a $500,000 Phase II NASA Innovative Advanced Concepts [NIAC] research award for their project, called In-situ Resource Utilization (ISRU) Based Robotic Construction Technologies for Lunar and Martian Infrastructure.

The moon has the potential to become a communications station, a staging area for expeditions to Mars, or a test site for missions to other planets, Khoshnevis says. Any of those applications will need landing pads and hangers for lunar landers, roads on which to transport the landers or equipment, storage facilities, and shade walls to shield sensitive equipment from the sun. (See “Moondust and More,” Civil Engineering, April 2006, and “Building on Mars,” Civil Engineering, October 2005.)

The team will spend two years proving the feasibility of robotically mixing concrete from lunar raw materials and building such structures by a process called “contour crafting,” a derivative of 3-D printing that Khoshnevis developed in 2000. Using contour crafting, concrete is robotically extruded, shaped, and smoothed under computer guidance.

The Phase II project is a continuation of the team’s Phase I NIAC project, which involved adapting Contour Crafting to lunar construction. The first USC proposal was one of 30 that NASA selected from a field of 800 in 2011 for a $100,000 Phase I award, and the Phase II proposal is one of just 10 that NASA selected from those original 30 plus other Phase I projects from previous years. Success with the Phase II project will put the USC team in the running for a Phase III NIAC grant.

To date, the USC researchers have successfully built walls and a small igloo-shaped structure using the robotic technology. But this is just the beginning, Khoshnevis says. He believes that combining lunar concrete with Contour Crafting will lead to almost limitless possibilities for lunar infrastructure construction.

He is confident that the contour crafting robots will perform as programmed. The question of finding a building material that is cost-effective for lunar use and can withstand extreme temperature differentials, micrometeorites, and solar and galactic cosmic radiation is more problematic. Lunar concrete fits the bill, Khoshnevis says.

“The cost of sending 1 kilogram of building material to the moon is more than $100,000,” he notes. “That means that using in situ materials is the only economic approach to building on the moon.”

The moon has a plentiful supply of regolith, or lunar sand, that can be used as a substrate for concrete, but the only water on the moon is contained in icy deposits in permanently shaded polar craters. The USC researchers will bypass the logistics of melting ice on the moon by developing two formulations of waterless concrete that use melted regolith.

Khoshnevis and his colleagues will test one mix made of sulfur and regolith. “Sulfur melts at 130° C, therefore it is very easy to turn the mix into a paste and extrude it,” Khoshnevis explains.
This would theoretically make sulfur-based lunar concrete an ideal material for contour crafting, except that it tends to clog the extruder because regolith is fairly abrasive. Another problem that needs to be solved, Khoshnevis adds, is preventing the concrete from melting under the direct sun on the moon, where the temperature can easily exceed 130° C.

The team will test a second formulation that uses only regolith. Regolith is a mixture of metal oxides and silica. Some metal oxide components can be melted at 1100° C to create a slurry using concentrated solar energy, microwaves, or laser energy. “The other components would stay in their solid form and serve as the aggregates in the mix, like gravel in concrete, and the components that melt would act like a binder,” Khoshnevis explains.

Engineering calculations for research purposes are based on estimated properties derived from simulated regolith provided by NASA and data that is already available about the moon surface. “The simulated regolith emulates what is on the moon, and there are considerable data available about moon rock,” explains Anders Carlson, P.E., S.E., M.ASCE, an assistant professor of architecture at USC. “Foundations are not a problem because the moon is solid, so settlement is not a concern.”

Still to be solved, Carlson says, is the issue of protecting structures from radiation. “Solar and galactic cosmic radiation is one of the biggest issues for any structures on the moon,” he notes. “The moon has just one-sixth of the earth’s gravity, so theoretically we can design slender structures with thin walls, but we need thicker walls to protect against radiation.”

Landing pads on the moon will present their own set of challenges, Khoshnevis adds. “The pad will have to withstand high-temperature exhaust from lunar landers and be surrounded by some type of blast area that will contain objects thrown by the force of the lander.” The USC researchers will collaborate with scientists at NASA’s Kennedy Space Center to solve these problems.

So, will the United States be building infrastructure on the moon in the next decade? It’s hard to say, says Carlson. “NASA is not concerned with meeting a particular deadline,” he says. “They are taking this process step by step.”


 

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