With NASA’s plan to send humans to Mars in the 2030s and SpaceX’s plan to send them as early as 2020, things are getting exciting. In just three years, the Mars 2020 astrobiology rover will blast off toward the red planet. While there, the rover will search for signs of life and gather information that will help protect the lives and missions of astronauts during future visits. The European Space Agency, in partnership with Roscosmos State Corporation, will launch the ExoMars rover in 2020 to undertake a similar mission. If SpaceX achieves its goal, humans could be visiting Mars at the same time as these rovers.
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| Artist’s concept of a future Mars mission. Image Credit: NASA/Pat Rawlings, SAIC. |
Today in the journal Scientific Reports, engineers from the University of California, San Diego demonstrate what could be a key building block for human shelters and infrastructure on Mars. Depending on the relative positions of the Earth and Mars, and the details of the orbit and spacecraft, the journey to Mars will take about eight months. Getting there requires lots of time, lots of money, and lots of risk. Once there, the astronauts will live and work in an environment that no human has encountered before. Access to suitable, easy-to-assemble, and plentiful building materials is not a simple need to meet.
Since they can’t very well carry lumber or bricks from the Earth to the landing site, ideally astronauts would build structures out of Mars-based resources. Researchers have proposed several clever possibilities, but until now they have required complex chemistry or energy-intensive processes. In this new work, Yu Qiao and his students show that you can make bricks—stronger than steel-reinforced concrete—with nothing but Martian soil and a little muscle.
The soil on Mars is a mixture of particles of volcanic rock, called basalt, and iron oxide—the compound that gives Mars its reddish color. Using Mars-1a soil, a material designed to simulate the chemical composition of the dirt on Mars, the team demonstrated that compressing the soil turns it into a rock-like solid that can be cut into bricks. It doesn’t take a ton of pressure—it’s similar to dropping a 10-lb weight on something from a height of about 1 meter.
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| One of the bricks made of Mars-1a soil compacted under pressure. It’s about 1cm wide. Image Credit: Jacobs School of Engineering/UC San Diego. |
Through a series of experiments, the researchers discovered that the iron oxide is key to forming these bricks. High-resolution scans show that the iron oxide particles, which are smaller than the basalt particles, coat the basalt particles under pressure and bind them together.
The researchers investigated how the strength of the bricks was affected by variables such as the method of applying pressure (gradually versus quickly), amount of pressure, average particle size, and type of container in which the sample was confined while compressed (rigid, free, or flexible). Note that these aren’t exactly normal-sized bricks, this work involved compressing small soil samples, creating bricks around an inch long. However, the results provide guidance for creating larger structures.
In the experiments, the researchers put the soil in a small cylinder and applied pressure with a piston. One of the most interesting results is that when confined in a rigid cylinder, the resulting bricks were not as strong as the those formed under much lower pressure in flexible cylinders. When free to expand laterally under gradual pressure, the resulting bricks were slightly stronger, but required much more pressure than those formed in flexible cylinders. These outcomes suggest that when the soil particles can move around during compression, the iron oxide can better coat the basalt and bind the material together.
The researchers say that the strength of the bricks can be increased by adding reinforcements, and that this method should be amenable to additive manufacturing, a technique in which you build up a large structure by forming the bottom layer and then adding additional layers one at a time. They have plans to study this in the near future.
“Mars is the next tangible frontier for human exploration, and it’s an achievable goal,” according to NASA’s Journey to Mars Overview. “There are challenges to pioneering Mars, but we know they are solvable. We are well on our way to getting there, landing there, and living there.”
—Kendra Redmond