NASA recently announced future rocket engines will include large scale 3D printed parts. A number of other companies are exploring how 3D printing additive manufacturing can be used in future space projects. One company, nTopology, developed software that seamlessly combines synthesized geometry and simulation for use with advanced manufacturing tools, such as additive technology. Ryan O’Hara, technical director of aerospace and defense at nTopology, discusses additive projects for the space and aerospace industry.
Additive manufacturing offers several benefits for aerospace and for space exploration. According to O’Hara, any land-based object and specifically any engineered part that goes into space is a combined part or assembly. Launching such a part into space ultimately requires a lot of money. While NASA is pushing for space exploration, you can only get so far with resources on earth. And there’s a limit to how far that can go.
But if parts are assembled on a forward basis, the task may be more manageable.
“I think space exploration becomes a logistics game,” said O’Hara. “I spent some time in the military, previously in the Air Force, and logistics is a huge part of any military operation. It’s the same for space operations; a big logistic scheme. Thus, the closer you can have your supplies to where you’re operating from, the better off you’ll be.”
Fundamentally, nTopology is a software company that focuses on advanced geometry, which handles some projects better than traditional design tools. O’Hara and his team are often approached to discuss space applications because people want to make their parts light, to reduce the cost of launching that object into space. Plus, there’s the potential to use minerals found on asteroids, moons, or different planets. Typically, that will require some advanced manufacturing method.
nTopology software would be categorized as generative design software. But the biggest different between nTopology software and other generative programs is that nTopology represents geometry with implicit math equations.
“Just like there are equations that describe simple objects like spheres and cubes,” notes O’Hara, “we can represent all types of geometry as implicit math equations. This makes it a lot easier to store an equation rather than the discretization of that geometry.”
Discretization means that rather than describing an object with facets, triangles, or other types of geometry, the description is a single equation that can be discretized into the shapes needed just before the program goes to the 3D printer. The discretization into an equation is done using procedural software.
Challenges of working with additive manufacturing for space
“Everybody’s always looking for a “magic pill” to make their designs better,” notes O’Hara. “I think the industry itself, in coordination with marketing teams, has maybe overplayed how simplistic things are in terms of achieving an optimal design. I think a big thing or focus that we have at our company is really the company name—nTopology, which is short for “any topology.” Our founder’s focus was to enable designers to be able to produce any geometry that they wanted or any topology. And I think that’s our core mission. And then we tie those things to simulation.”
Combining topology optimization and simulation lets designers optimize for various factors including stress.
“But a key thing is that even though we enable any topology, we don’t replace the designer,” adds O’Hara. “We just remove barriers to the designer to make geometry. I think that’s a fundamental difference for us. I think it would be silly for us to assume that a designer with 20 years of experience on space applications, or I don’t know, reactors for power generation in space that involve radiation, it would be silly for us to think that we can just replace that person with an algorithm. But if they need geometry that can take their designs to the next level, that’s really what we wanted to enable.”
One of the examples relevant to space is the design of heat exchangers. In space, managing heat is important but there’s a primary difference. “Oftentimes you do not have an atmosphere, right,” notes O’Hara. “There are three primary methods for exchanging heat: convection—air or fluid moving over an object; radiation – actually radiating heat away; and conduction. So now you may have to be more strategic and more involved on the design process to account for the missing physics not available because you’re in space without atmosphere.”
O’Hara and his team have been exploring the geometries available for heat exchangers. One of the geometries is known as triply periodic with minimal surfaces, which are a combination of sines and cosines in space. They represent a curvy shape with passages inside. The key is that they have two domains, a hot side and a cold side.
“We’re finding that these provide incredible capability to exchange heat, more so than a traditional what we would call a ‘tube in shell.’”
(A traditional heat exchanger typically has tubes inside and then passes either a hot or cold fluid. The tubes are surrounded by an outer chamber that usually flows a cold fluid. These simple geometries are easy to manufacture, but they don’t necessarily maximize the space associated with a volume.)
“Our traditional topology optimization program produces shapes that look bio-inspired or organic. Our representation of geometry is really great for repeating structures, such as a Nautilus type geometry with a helix or a spiral shape. Inside of that spiral shape are chambers. A helix is really just a combination of sines and cosines, in this case in just two dimensions, typically in the X and Y. If you combine that in the third dimension, then we can really make good use of space. But the traditional topology optimization uses an algorithm that tries to maximize stiffness of a part. And that stiffness, when you perform this operation, actually allows you fundamentally how to visualize the load path of an object.
“And then using that algorithm, we can put material where it needs to be. Our approach to representing those geometries covers that span of macro to micro scales.”
Additive benefits in space and aerospace defense exploration
One of the bigger benefits of using additive manufacturing in space is the ability to make parts with material on hand, which affects logistics.
“We’re not going to be able to take all the material that we need with us into space. So, you’re going to have to use the resources that are available. We’re probably not going to be able to build a steel mill on Mars. Maybe astronauts just set up a crude base. But maybe the manufacturing material is produced with rock from Mars, ground up and powderized, and then bound together with some sort of a binder. Or maybe the material is melted together if there are more metal compounds. Additive manufacturing, I think, will be key in being able to leverage resources that are readily available to those space explorers.”
Even though there are plenty of hurdles with manufacturing in space, the market is exploding, with small, private companies filling the niches. O’Hara sees the use of additive manufacturing to help produce rockets that can launch into space as a democratization of space exploration. Looking ahead, is there a way to leverage additive in the logistics game?
O’Hara’s team is exploring topology optimization where parts have biological, organic shapes using additive manufacturing where it’s complimentary. One example is a sand-casting mold for a foundry operation. They will pour aluminum in a mold made through additive manufacturing. The mold will be a combination of sand in epoxy binder. Such processes will likely be used in space applications where you’re binding a core material together to produce a part.
Says O’Hara, “In terms of space and advanced manufacturing, there’s a lot of capability that’s available today. I think maybe the biggest hindrance to adoption that I see is just people’s willingness to explore these new technologies versus the traditional “way we’ve always done it.” I think the future lies in engineers being bold and exploring both new design capabilities and new advanced manufacturing capabilities to enable the future.”
