These 3D printed engines can power space-bound rockets—or hypersonic weapons

In Overmatched, we take a close look at the science and technology at the heart of the defense industry—the world of soldiers and spies.

ON THE COLORADO PLAINS just below the Rocky Mountains, near the quaint town of Berthoud, lies the headquarters of a space company called Ursa Major. There, just about an hour’s drive north of Denver, the company regularly test-fires rocket engines straight out the back of an onsite bunker. 

These engines, which are mostly 3D printed, aren’t just for launching satellites into space: They’re also of interest to the US military for propelling hypersonic vehicles. And their dual-use nature is a modern manifestation of the two faces that rocket technology has always had, which is that it is simultaneously useful for defensive and offensive purposes, and for cosmic exploration.

With this technology in hand, the company hopes to get both civilian and military projects off the ground.

3… 2…1… liftoff

Joe Laurienti, who founded Ursa Major in 2015, grew up not too far from Berthoud. His father worked for Ball Aerospace—the cosmic arm of the company that makes a whole lot of aluminum cans, and the former owner of Ursa Major’s current 90-acre site. “He was always working on satellites,” says Laurienti. But when Laurienti went to see one of his father’s payloads launch, he thought, “The thing my dad worked on is really important. It’s on top of this rocket. But the fire coming out the bottom is way more exciting.”

Laurienti has been chasing that fire ever since, his life consumed by propulsion: the technology that makes rockets go up fast enough to counteract gravity and reach orbit. As an adult, he joined SpaceX’s propulsion team, then slipped over to Blue Origin—hitting two of the trifecta of space-launch companies owned by famous billionaires. (The third is Richard Branson’s Virgin Galactic.)

Soon, Laurienti saw others in the industry trying to start commercial rocket companies. He, perhaps biased, didn’t think that was a good idea: The heavy hitters that were founded first would obviously win, and the others would just be also-rans.

Nevertheless, he thought he had a startup to contribute to the mix: one that wouldn’t make entire rockets but just engines, to sell to rocket companies—much like General Electric makes engines that propel aircraft from Boeing or Airbus. “I spent my career on the engines, and that was always kind of a pain point” for the industry, says Laurienti.

Rocket engines, of course, are pretty important for heaving the space-bound vehicle upward. “A little over 50 percent of launch failures in the last 10 years are propulsion-related,” explains Bill Murray, Ursa’s vice president of engineering, who’s known Laurienti since they were both undergrads at the University of Southern California. You can take that to mean that half the complexity of a rocket exists inside the engines. Take that out of some rocket maker’s equation for them? Their job theoretically gets a lot easier.

“That’s the next wave of aerospace,” thought Laurienti. “It’s specialization.” 

With that idea, he sold his SpaceX stock in preparation for his new venture. “Instead of buying a house and starting a family, I bought a 3D printer, started the company, and made my mom cry,” he says.

rocket engine test
Testing an engine called Ripley. Ursa Major

3D printing engines—and entire rockets

The 3D printer was key to Laurienti’s vision. Today, 80 percent of a given Ursa engine is 3D printed with a metal alloy—and printed as a unit, rather than as separate spat-out elements welded together later. Most space companies use additive manufacturing (another way to refer to 3D printing) to some degree, but in general, they aren’t 3D printing the majority of their hardware. And they also aren’t, in general, designing their space toys to take advantage of 3D printing’s special traits, like making a complicated piece of hardware as one single part rather than hundreds.

That kind of mindset is also important at another company, Relativity Space, which has 3D printed basically an entire rocket—including the engines. Its Terran 1 rocket is the largest 3D printed object on Earth. The team attempted to launch the rocket on March 8 and 11, but it ultimately scrubbed the shots both times due to issues with ground equipment, fuel pressure, and automation systems.

Like Laurienti, Relativity founder Tim Ellis noticed a reluctance to fully embrace 3D printing tech at traditional space companies. At Blue Origin, his former employer, Ellis was the first person to do metal 3D printing; he was an intern desperate to finish creating a turbo pump assembly before his apprenticeship was over. Later, as a full employee, Ellis would go on to start and lead a metal 3D printing division at the company. 

But the way traditional space companies like Blue Origin usually do 3D printing didn’t work for him, because he felt that it didn’t always include designing parts to take advantage of additive manufacturing’s unique capabilities. “Every 3D printed part that Relativity has made would not be possible to build with traditional manufacturing,” says Ellis. The result of that approach has been “structures that ended up looking highly integrated, [because] so many parts of our rocket engine, for example, are built in single pieces.” Those one-part pieces would, in traditional manufacturing, have been made of up to thousands of individual pieces.

He thought more people would have come over to this side by now. “It’s been a lot slower than I’ve expected, honestly, to adopt 3D printing,” he says. “And I think it’s because it’s been slower for people to realize this is not just a manufacturing technology. It’s a new way to develop products.”

Five times the speed of sound

Initially, Ursa Major’s business model focused on space launch: getting things to orbit, a process powered by the company’s first engine, called Hadley. The design, currently still in production, slurps liquid oxygen and kerosene to produce 5,000 pounds of thrust. That’s about the same as the engines on Rocket Lab’s small Electron vehicle, or VirginOrbit’s LauncherOne spaceplane. 

But then an early customer—whose name Laurienti did not share—approached the company about a different application: hypersonics. These vehicles are designed to fly within Earth’s atmosphere at more than five times the speed of sound. Usually, when people discuss hypersonics, they’re talking about fast-moving, maneuverable weapons. 

“Hey, we were buying rocket engines from someone else, but they’re not really tailored for hypersonics,” Laurienti recalls this customer saying. “You’re [in] early development. Can you make some changes?” 

They could, although it wouldn’t be as easy as flipping a switch. Hypersonic vehicles often launch from the air—from the bottom of planes—whereas rockets typically shoot from the ground on their way to space. Hypersonics also remain within the atmosphere. That latter part is surprisingly hard, in the context of high speeds.  

Just like rubbing your hand on fabric warms both up, rubbing a hypersonic vehicle against the air raises the temperature of both. “The atmosphere around you is glowing red, trying to eat your vehicle,” says Laurienti. That heat, which creates a plasma around the craft, also makes it hard to send communications signals through. Sustaining high speeds and a working machine in that harsh environment remains a challenge.

But the company seems to have figured out how to make Hadley, which is now in its fourth iteration, work in the contexts of both launching a rocket to space and propelling a hypersonic vehicle that stays within Earth’s atmosphere. As part of one of Ursa Major’s contracts, the military wanted the engine to power an aircraft called the X-60A, a program run by the Air Force Research Lab. The X-60A was built as a system on which hypersonic technologies could fly, to test their mettle and give engineers a way to clock the weapons’ behavior.

Hypersonic weapons—fast, earthbound missiles—aren’t actually faster than intercontinental ballistic missiles (ICBMs), which carry nuclear warheads and arc up into space and then back down to their targets. But they’re of interest and concern to military types because they don’t have to follow trajectories as predictable as ICBMs do, meaning they’re harder to track and shoot down. Russia, China, India, France, Australia, Germany, Japan, both Koreas, and Iran all have hypersonic weapon research programs.

To intercept these fast-moving weapons, a country might need its own hypersonics, so there’s a defensive element and an offensive one. That’s partly why the Department of Defense has invested billions of dollars in hypersonics research, in addition to its desire to keep up with other countries’ technological abilities. That, of course, often makes other countries want to keep pace or get ahead, which can lead to everyone investing more money in the research.

A long-standing duality

Rocket technology, often touted as a way for humans to explore and dream grandly, has always had a military connection—not implicitly, but in a burning-bright obvious way. “[Nazi Germany’s] V-2 rocket was the progenitor to the intercontinental ballistic missiles,” says Lisa Ruth Rand, an assistant professor of history at Caltech, who focuses on space technologies and their afterlives.

Space-destined rockets were, at least at first, basically ballistic missiles. After all, a powerful stick of fire is a powerful stick of fire, no matter where it is intended to go. And that was true from the Space Age’s very beginning. “The R-7 rocket that launched Sputnik was one of the first operational ICBMs,” says Rand. The first American astronauts, she continues, shot to space on the tip of a modified Redstone ballistic missile. Then came Atlas rockets and Titan rockets, which even share the same names as the US missiles that were souped up to make them.

Rockets and flying weapons also share a kind of philosophical lineage, in terms of the subconscious meaning they impart on those who experience their fire. “They really shrunk the world, in a lot of ways, in time and space,” says Rand. “Accessing another part of the world, whether you were launching a weapon or a satellite, really made the world smaller.”

Today, in general, the development of missile technology has been decoupled from space-launch technology, as the rockets intended for orbit have been built specifically for that purpose. But it’s important not to forget where they came from. “They still all descend from the V-2 and from these military rockets,” says Rand. “And also most of them still launch DOD payloads.”

In a lot of ways, a 3D printed rocket engine that can both power a hypersonic vehicle and launch a satellite into orbit is the 21st-century manifestation of the duality that’s been there from the beginning. “Maybe it’s just saying the quiet part out loud,” says Rand. “What’s happening here—that was always kind of the case. But now we’re just making it very clear that, ‘Yeah, this has got to be used for both. We are building a company and this is our market and, yes, rockets are used for two main things: satellites and launching weapons.’”

rocket engine test
A fiery scene in Colorado: The Ripley engine fires. Ursa Major

‘A shock hitting your chest’ 

It’s no surprise that hypersonic capabilities have gotten their share of American hype—not all of it totally deserved. As defense researchers pointed out in Scientific American recently, the US has for decades put ballistic missiles on steerable maneuvering reentry vehicles, or MaRVs. Although they can only shift around toward the end of their flight, they can nonetheless change their path. Similarly, the scientists continued, while a lower-flying hypersonic might evade radar until it approaches, the US doesn’t totally rely on radar for missile defense: It also has infrared-seeking satellites that could expose a burning rocket engine like Hadley.

Still, the Air Force has been interested in what Ursa Major might be able to contribute to its hypersonic research, having funded seven programs with the company, according to the website USA Spending, which tracks federal contracts and awards. In fact, the Air Force is Ursa’s only listed government customer, having invested a few million in both the hypersonic and space-launch sides of the business. It’s also responsible for two of four of Relativity’s federal awards. 

Also of national security interest, of late, is decreasing the country’s reliance on Russian rocket engines for space launch. To that end, Ursa Major has a new engine, called Arroway, in development, which boasts 200,000 pounds of thrust. “Arroway engines will be one of very few commercially available engines that, when clustered together, can displace the Russian-made RD-180 and RD-181, which are no longer available to US launch companies,” the company said last June. It is also developing a third, in-between engine called Ripley, a scaled-up version of Hadley. 

Today, Ursa Major tests their 3D printed engines up to three times daily. On any given day, visitors in Berthoud might unknowingly be near six or nine high-powered experiments. When the static rocket engine begins its test, huge vapor clouds from the cryogenics can envelop an engineer. 

“When it lights, it’s just a shock hitting your chest,” says Laurienti. A cone of flames shoots from the back of the engine, toward a pile of sand in the field behind the bunker. Onlookers face the fire head-on, their backs to the mountains and their eyes on the prize.

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Sarah Scoles

Contributing Editor

Sarah Scoles is a freelance science journalist and regular Popular Science contributor, who’s been writing for the publication since 2014. She covers the ways that science and technology interact with societal, corporate, and national security interests. The author of the books Making Contact, They Are Already Here, Astronomical Mindfulness, and the forthcoming Mass Defect, she lives in Denver and escapes to the mountains to search for abandoned mines and ghost towns as often as she can.