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One of the most fascinating technologies to be birthed out of the turn of the millennium is additive, or 3D, printing. And like many other scientific discoveries and inventions, it doesn’t take a ton of imagination to see how something like that might be useful in space. In fact, I would argue that in order for something like a colony/generation ship to be successful, it would absolutely need to have the ability to manufacture new parts on the spot.
Why do we need something like 3D printing for this? Resupply. In most manufacturing instances, if a part breaks, you can order a new one. Even with a situation like a colony on Mars, ordering a replacement part from Earth is feasible, even if it does take several months for delivery. (Seriously, Amazon? What happened to my 2-Day shipping?) However, in the deep black of the interstellar medium, I’m afraid your only shipping options are “Never” and “30 Years After You Get To Proxima Centauri.” And, to be honest, neither of those options are terribly attractive.
So, as the engineer on a massive hunk of hollow metal hurtling through space filled with a few thousand souls, what you need is the ability to make parts? A full machining shop seems a bit over the top, especially when you start thinking how much space and weight are at a premium on a ship like that. But what if you could have a stockpile of raw material then just shape it into whatever you need when you need it? That’s exactly what 3D printing can do.
NASA has already shown interest in this technology. Recently, astronauts aboard the International Space Station performed tests using a 3D extrusion printer as part of a partnership with Made in Space, Inc (MIS), a NASA Small Business Innovation Research contractee. In this test, they printed various objects multiple times and tested strong, flexible, compression resistant and shear resistant the objects were. MIS then compared that data to ground-based printed versions of those objects. The results were somewhat mixed. While the objects printed in space came out just fine, their strengths and weaknesses varied some from their ground-printed counterparts. The results report seems to indicate that at least part of that was due to a difference in the material density in zero-G/microgravity versus on the ground. However, the testing team did create a robust Lessons Learned section in their report and show promise for transitioning to having a full 3D printing machine shop in space in the not too-distant future.
So, NASA has tested some additive printing in space, but they’ve only tested one type. And that type may not be the best for the long-term. In fact, there are around seven different types of 3D printing technology. What makes each type different is how the three-dimensional object is made, including Stereolithography, Digital Light Processing, Fused deposition modeling, Selective Laser Sintering, Selective laser melting, Electronic Beam Melting, and Laminated object manufacturing (LOM). For starters, most additive printers print in three dimensions—up/down, left/right, forward/backward—by starting at a single point and making a line. This is our X-axis, or left/right. That’s one dimension. Then, they add another line next to it, and another, and another. This is our Y-axis, or forward/backward. This gives us a flat shape. And that is two dimensions. Finally, the printer begins another layer on top of that one (or beneath it, in some cases). This is our final Z-axis, we’ll call it up/down. This vertical direction is what makes the object three dimensional.
Each of the different types of printers comes about creating those layers in different ways. A lot of commercially consumer printers use a variation of Fused Deposition Modeling. This technology uses a filament of material that is fed through a printhead. The printhead then liquefies the filament and extrudes it out onto the build platform. Like a traditional printer, the head moves left/right and forward/backward, but the build platform itself usually moves in the up/down, allowing the printhead to have room to print another layer on top.
Other types of printing use various twists on this format, but one of the more interesting ideas that has so far one of the fastest and most precise, is called CLIP, Continuous Liquid Interface Production, created by a company called Carbon. Somewhat similar to the 3D printing tech called stereolithography, CLIP uses a liquid material that is photoreactive, meaning it hardens with light. What makes it different is that the production process is closer to growing rather than printing. A CLIP machine projects the entire layer of an object into a liquid material. However, instead of doing one layer at a time, the projection actually shifts, allowing the build platform to be pulled from the liquid smoothly and continuously. There’s a whole lot more technology and chemistry that goes into it, but that is the gist of it for the most part. (Check out this video demo on CLIP)
So, why CLIP for space and colony ships? Most forms of 3D printing can take several hours—read 3 for small, simple items to 36 for larger and/or more complex pieces—to produce a single part. But CLIP can produce complex structures in less than twenty minutes. There are some hurdles though. Currently, using a fluid can be messier and harder to control in a zero-G environment. If those hurdles can be overcome though, the speed, precision, and range of materials could be far more valuable.
And, since we talk about science fiction here, let’s look at how those issues with CLIP might be overcome. In fact, I think there might be a way to keep it cleaner and easier to control in one fell-swoop with just one word. Sound.
Remember a few years ago when the video of scientists making water droplets float in mid-air went viral? (If not, check it out right here.) Well, they did it with sound. The idea was that sound waves tuned just right were able to cancel out the effects of gravity for materials around the density of water. Sure, CLIP material liquids would likely be much denser than water, but with some tweaking, couldn’t we make this apply? And, since acoustics can cancel out gravity, they should be able to replicate it in some fashion, too.
So here’s the idea. In a vat filled with the CLIP material fluid, an advanced version of one of the Carbon’s machines creates an item. But, to keep the fluid under continuous pressure, so it doesn’t slosh around and what not, an acoustic plunger or wall keeps the liquid together. Then, when the object is done printing, the printing platform is pulled through the acoustic wall, almost like a forcefield. This strips off most of the excess liquid and keeps the rest of the non-cured material in place.
Boom! Super-precise, fast, layerless 3D printing in space. You’re welcome.
Seriously, though. This kind of technology would make part replacement incredibly efficient. Even outside of a colony ship, using something like this in deep space could make ships extremely resilient. Imagine being able to just stop by an asteroid and pick up some new raw material then printing it into parts. Obviously, that presents a whole new level of issues, but I think we can overcome them and turn our solar system’s left over trash into a vast trove of raw materials.
Post-Note: Currently, CLIP’s material capabilities does not include metals, though I could imagine this changing at some point. Even if it doesn’t, though, there are other technologies capable of making high-precision parts extremely quickly. Desktop Metal’s system is one example. DM’s machines use small rods made of metal and polymer binding to print out a shape. The printed object then goes through a bath to get rid of most of the binding material. The final phase is a furnace built into the machine which burns away the remaining binder and fuses the remaining metals into an extremely (read 99.8%) dense object. As a more-standard extrusion-based 3D printer, DM’s machine might be more easily configured to microgravity environments for parts that require metal.