Words by Matthew Troemner
Any Martian settlement will need 3D-printed homes
Our team at Northwestern University is taking part in NASA’s 3D-Printed Habitat Challenge, exploring additive construction technology to create housing for deep-space exploration, including its 2033 mission to Mars. If you’re going to Mars for any extended period of time, it doesn’t make sense to send all of your resources from Earth — the transport costs would be enormous. So you have to produce habitats and structures using what’s already there on the planet’s surface, through 3D-printing or another manufacturing process.
Mars is the ultimate material efficiency challenge
We’re using a concrete based on sulfur. Sulfur is readily available on Mars, and it doesn’t need water. There is frozen water within the planet’s surface, but you’ll need that to live on, so we didn’t want to utilize such a precious resource as a building material. For testing, we’re mixing it 50/50 with a basalt-based simulant from the Mojave desert, which has an 80-90% chemical match to Martian rock. Silica-sand sulfur concrete was explored in the 1970s and 80s, but it’s notably stronger when using Martian-like soil. Our next step will be to perform a scanning electron microscope study so we can see why that is.
Building is quick — it’s the scavenging that’ll take time
Our system is extrusion-based, like plastic injection moulding. The sulfur and Martian soil are retrieved by robotic scavengers and combined in a screw that’s heated to above the melting point of sulfur — about 130-140ºC. Then it’s pushed out as a semi-solid concrete, similar to the consistency of toothpaste. As soon as it cools below melting point, you have a solidified structure that you can print on top of. For the NASA competition, teams have 30 hours to print a 1:3 scale model. So multiplying that up, you could theoretically print a complete habitat in a couple of weeks on Mars, not factoring in dust storms or other real-world conditions.
Astronauts need homes, not just protective shells
We’ve talked with many designers and even neurobiologists to figure out what should go into a Martian habitat. The NASA competition envisages four astronauts living for one year in what is essentially a 1,000ft2 apartment — a lot of people in a very small area. So the last thing you want is an overly scientific or sterile atmosphere. It needs to be appealing to the eye, with some of the colours, textures and comforts you’d find in a regular home. We could bring some collapsible furniture from Earth, but also 3D-print smaller objects using polyethylene recycled from the spacecraft, whether that’s drinking glasses or interior window panels.
Marscrete could be a low-carbon alternative on Earth
Everything that we’re putting into this material is found on Earth, so you could have sulfur-based, 3D-printed structures here. Sulfur is a by-product of oil production, so you can get it for almost nothing. Marscrete is cheap, strong and has a much lower environmental impact than Portland cement-based concretes. It doesn’t have all the benefits of regular concrete — it’s not fire resistant — but there are definitely potential applications.
Matthew Troemner is part of the Martian 3Design research team at Northwestern University, Illinois