In the last two decades, 3D printing technology has transformed from a sci-fi concept into an everyday aspect of life. One idea rapidly gaining traction focuses on the use of 3D printers to build homes and facilities on Earth and in space. However, making it a reality might be more difficult than it seems.
How 3D Printing Works
Even twenty years ago, the idea of creating, say, a teacup, in the comfort of your own home with a simple command prompt, seemed impossible. But engineers have dedicated years of hard work to make it a reality. Thanks to their efforts, this technology is no longer the purview of professional workshops — now we can use 3D printers right in our homes.
From a technical standpoint, 3D printers are a type of computer numerical control (CNC) machine. The classification applies to production tools using digital models without human assistance.
These CNC machines are run on software that controls a specific tool-set and follows the digital model parameters of the end product. An example of this would be a CNC milling machine that cuts flat or three-dimensional objects from a given material. This is exactly how we get plywood fridge magnets.
In a complete reversal of this process, 3D printers operate by creating an object at specific coordinates instead of cutting it from materials. Typically, these printers use a form of fast-cooling liquid or paste-like substance that sets into a desired shape.
There are many varieties of 3D printing, each with its own advantages and drawbacks, and each following a specific process. Such diversity allows for printing with materials other than plastic, namely ceramics, concrete, and even metal.
Can We Really Print a House?
Following the success with creating small objects, many engineers began contemplating the idea of large-scale 3D printing CNCs. For instance, using them to print entire buildings. The reason behind this choice is rather obvious: facility construction, while a relatively simple concept, remains a time-consuming, labor-intensive, and therefore costly process.
The main advantage of 3D construction printers is their ability to reduce both labor costs and production time. Though development of these machines began around ten years ago, yielding first prototypes soon after, it never moved beyond the experimental phase.
There are a number of aggravating factors behind this delay, all connected to the scale-up problem: after all, a tiny decorative item is vastly different in size and application from a three-story building. By examining the upsizing issue, we can also understand how it affects the entire concept at large.
The Problem with Frames
A 3D printer’s body needs to be fixed in place, so it could move freely within three dimensions and cover a specified area. Within that area, its nozzles follow a set of coordinates as per the digital model.
Home 3D printers typically use a nozzle that slides within a frame right to left, back and forth, up and down. In most cases, the end product remains within this frame and often inside the printer’s body itself.
Now imagine the same process but for a five-story building. In this case, a printer’s frame needs to be greater than the planned building, and the nozzle itself needs to be considerably upscaled. If that’s not enough, the entire structure has to remain stable under its own weight, which is bound to be massive.
Additionally, the frame components require powerful and complex electric motors to move them in specified positions. In turn, the motors will need a consistent source of power and regular maintenance, which means that mechanics and electricians will have to climb pretty high up to service them.
But the most noteworthy difficulty with upscaling comes at the end, when it’s time to remove the ready product. With home-use 3D printers, you can simply open the frame and take out the printed component. Obviously, you can’t do it with a building. Nor can we leave it as is, considering that the printer might be needed elsewhere to commence work on the next building. And in standby, it can only be a hazard.
As it stands, to print a building, you would need to assemble and calibrate a massive production system. This means that its ability to print a house “without human assistance” is rather limited. Moreover, after the process is complete, the entire production set-up will need to be disassembled. It goes without saying that larger buildings directly impact the overall cost.
What Do We Build From?
Before we could start printing houses, we first need to tackle the question of suitable building material. Plastic, which is widely used in home 3D printers, seems like the simplest and most logical option for building.
Plastic is easy to melt and harden, but its many advantages are overshadowed by one huge drawback — its high cost. Any potential savings from low labor expenses would be sapped by the cost of materials. So the idea of using plastic to print support structures spanning hundreds of cubic feet simply makes no sense.
Metals and basalt are another option. While the former are more durable and also more expensive, the latter is more affordable but naturally more fragile. Still, they both have the same pros and cons: on the one hand, it’s durability; on the other, it increases both the weight and overall cost. What complicates the process even further is the fact that these raw materials come in powder-like form, which then needs to be fused with lasers.
A somewhat easier process is clay extrusion. This method is similar to plastic printing, except in this case the main problem is water-resistance. Considering that the building needs to be as weatherproof as possible, rain and all, the clay has to undergo intense heat treatment during printing. In other words, we need to bake it. This comes with huge energy costs, not to mention the clay walls might crack from the heat while still in printing.
The most popular 3D construction material to date is concrete — a composite of hard silicates in the form of sand particles and crushed stone that are “glued” into a slurry with cement.
In terms of strength and durability, concrete is rather average compared to other known adhesive materials. But it’s also pretty cheap. None of its alternatives even come close to the ratio of effectiveness and affordability found in concrete, which is why it’s the most widely used building material in the world.
The Problem with Concrete
By now, we have mastered the ways to control concrete composites. So it won’t pose much of a challenge to formulate a mixture that’s hard enough for 3D printing layer by layer, the same way it’s done with plastic.
However, concrete has one particular, and by now well-known, property that could make its use in 3D printing problematic. While its ability to withstand compressive forces is remarkable, concrete is much worse at elasticity. And its lackluster performance against elastic forces occurs in very unexpected places.
As each bend in the main structure generates elastic force, it stresses the material. So even if we place a window or door opening to mitigate this, the concrete, once hardened, might crack anyway under its own weight.
The only solution is to design arched windows, similar to the ones you see in older buildings, but that would require increasing the overall height of the structure.
Ceilings raise the same problem. To maintain integrity, ceilings need to be either extremely thick and heavy, or have a vaulted or arched design. And again we face the issue of overall cost: all these design considerations add to construction expenses while reducing livable and utility space.
For conventional construction methods, this problem has long been solved with metal rods that are installed at the points of tension in the concrete structure. In other words, reinforcement. Hence the name — reinforced concrete.
Unfortunately, we can’t apply the same solution for 3D-printed buildings. The rods have to be installed manually, and for large structures this means the use of cranes, which completely undermines all CNC advantages.
The Problem with Foundation
Another major obstacle that prevents us from 3D printing a house on the spot is the weight of the building, typically measured in tons. In most cases, simply installing the walls won’t work — the structure will start sinking, and you’d be lucky if that happens at an even rate. And if it doesn’t sink, it will likely crack.
To prevent this, a building must be stabilized on a foundation designed to transfer the load to the pre-compacted soil. Before laying the foundation, you need to make sure the geology of the soil underneath is compatible and reinforce the base. Or simply wait for more favorable conditions. This process is usually much longer than it takes to build the walls, and using a 3D printer rarely speeds it up.
All of this essentially negates most advantages of using 3D construction printers on Earth. After all, it won’t matter that walls can be built in six days instead of the conventional six weeks, if the foundation still takes six whole months.
What 3D Printers Can’t Do
Another reason that 3D-printed houses remain an experimental concept lies in the fundamental complexity of construction as a process. Laying the foundation and erecting the walls is barely scratching the surface of what goes into building a house.
Even after the roof and walls are completed, work carries on; this includes piping, sewage, electrics, and communications. While not that resource-heavy, they demand high precision, and at the current point of development, 3D printing is incapable of performing them at that level.
The same goes for doors, windows, interior walls and ceilings. Modern buildings require lighting, air conditioning, and other life-sustaining systems. Yet again, 3D printers aren’t quite there yet.
Why Building in Space Is So Challening
All of these concerns mainly apply to construction on Earth. In space, conditions are drastically different. Construction in general should be approached from a different angle based on its location in space, whether it’s another celestial body or various orbits. And based on our experience with lunar construction, we are already facing a number of potential issues.
The first and main obstacle in most off-Earth locations is human limitations. Human workers face a number of difficulties when conducting operations in vacuum or thin atmosphere. Despite our decades-long experience of building in orbit, all extravehicular activities on the ISS are meticulously pre-planned.
Construction on Earth owes its success to the mass deployment of experts and labor force. They are able to dedicate hundreds of combined man-hours to the project, week after week, all the while utilizing a variety of tools and methods.
In space, welding still remains one of the hardest operations to perform. So much so that it hasn’t moved beyond its experimental phase for many decades now. When astronauts conduct EVAs, they typically connect made-to-match components. All they need to do is screw in nuts and bolts, and connect wires to sockets.
By using the same approach, we could theoretically build a small settlement on the Moon. Most plans for lunar construction involve this exact “build on Earth and launch into space” concept. But this method has certain limitations, mainly its astronomical cost. And the farther we move from Earth, the higher these expenses will mount for each pound of material used to build our tin-can-sized living modules.
Given how restrictive these modules are, any long-term habitation will require further expansion of facilities. Engineers are already looking for solutions, in particular whether it would be possible to use the Moon’s natural resources.
What Makes Lunar Construction Unique
When it comes to building on the Moon, there are a number of factors that define what is exactly possible to achieve there. For one, building foundations on the Moon, and several other bodies in the Solar System, is impossible, at least the way we do it on Earth. The Moon has neither tectonic activity, nor sedimentary rock that could sink under an object’s weight. So on our satellite, this part of construction could prove to be simpler.
Similarly, the Moon has no weather to account for, whether it’s rain or wind. Plus, windows as a light source wouldn’t make any sense. What we would need is to shield the facilities with a layer of lunar rock for protection against radiation and micrometeorites.
Another important distinction arises in the way concrete behaves on the Moon — in vacuum, the water evaporates, rendering the mixture unusable, unless handled in specially equipped sealed environments. In addition, the Moon lacks the type of rocks suitable for cement production. Considering how all of this hinders traditional construction methods, 3D printing might get a chance to shine.
Selecting 3D Printing Materials for Space
In designing tools for space, manufacturers of 3D construction printers face the major dilemma — finding building materials. As already mentioned, Portland cement concrete can’t be used in vacuum due to water evaporation, so the only way to work with it is in airtight environments.
There are two possible solutions to this. The first is to formulate a composite from crushed lunar rock and adhesive solutions from Earth. The resulting mixture needs to be capable of polymerization, without water or atmosphere to aid it. Such mixtures already exist, but their high cost limits their application on Earth. However, on the Moon, using such expensive composites would be completely justified.
The second solution involves melting lunar rock and other minerals for use in 3D printers. This could be achieved with a printing tool that draws powderized material from a built-in storage and applies lasers to fuse it at specified points.
Compared to synthetic substances, basalt shows even more potential as a building material for 3D printers in space. Despite the major energy costs involved, this method could yield materials capable of withstanding elastic forces, thus eliminating the need for additional reinforcement.
Frameless 3D Printers
Using 3D printers on the Moon is significantly less complicated than on Earth. Lacking any atmosphere, the Moon also has no wind. Moreover, its gravity is six times weaker compared to what we are used to on our planet. This means that a lot of frame-related issues are more manageable. Here, 3D printer frames could be lighter and taller, relative to what we are accustomed to.
That said, our airless satellite poses other difficulties for construction, namely its automation. Robots are a far better option than humans for carrying out any work on the surface. One way or another, we will have to design construction robots for performing a series of processes following 3D models.
So why not make these utility robots capable of melting lunar rock and creating structures according to digital models? In essence, they will act as operational tools of a frameless 3D printer. In order to traverse the surface, these robots will need to be equipped with extendable legs, or even rocket engines.
It might sound like something straight out of science fiction, but Earth already has a natural equivalent of these self-propelling 3D printer nozzles. They are wasps, of course. These tiny creatures construct nests by milling wood with their tiny jaws and transforming it into adhesive paper. Once again, we might follow nature’s footsteps and use this knowledge to build our own lunar nests.
It’s not only wasps that could give us a few tips, but their nests as well. On the Moon, any large-scale construction must follow two key principles. First, the facilities must maximize volume while minimizing surface area. Second, they have to be protected from radiation with layers of lunar rock.
The best design to fit these criteria is a shallow dome. Its shape helps distribute the overall load while ensuring substantial interior volume. Moreover, this type of shape is more convenient for 3D printing layer by layer, following a digital model.
In conclusion, unlike Earth, 3D printing in space shows significant potential, in terms of both implementation and further development.
Returning to Earth
Once we have mastered this technology in space, it’s quite possible we could adapt it for use on Earth. There is more than one precedent for this in the past. As for the funding, the main areas that will likely require considerable investments include research and development as well as experimental stages and production of robot-workers.
As soon as these robots become available for mass production, it’s entirely possible that, in the future, they could also be applied on Earth. Who’s to say, we could even adapt them for use with regular concrete instead of basalt, possibly introducing a new 3D printing method for building new houses across the world.
