Jeff Thornburg has worn many titles: SpaceX propulsion chief, Amazon Kuiper executive, and now CEO of Portal Space Systems. In the first part of this series, he explained how falling launch costs and shelved government R&D are reshaping the business of space. In this second part, the focus shifts to the engineer in him, and the technology he says changed rocket design forever: 3D printing.
Portal itself is built around that same philosophy. Its Supernova spacecraft is designed to move quickly across orbits, powered by a solar-thermal propulsion system called the HEX thruster. Just last month, Portal proved that thruster in vacuum conditions; the first commercial success for this type of propulsion, made possible by 3D printing.
Portal’s HEX thruster.
Thornburg still remembers the frustration of building rocket engines the old way. Castings took months, sometimes years, and even then, they were “riddled with defects.”
“You’d do a casting run of 15 and only 2 were usable,” he recalls. “It was like an art form. And I thought — this is really how we’re running the railroad?”
Then came metal 3D printing. For Thornburg, it was a revelation. Instead of waiting a year or two for castings, he could get a part in days. Complex parts could be built in hours, not years. Additive manufacturing, he says, was never a side experiment. It became indispensable.
Supernova spacecraft.
Castings Out, Monoliths In
“Castings are so problematic in aerospace, especially in high-pressure components,” Thornburg explains. They were slow to produce, full of defects, and required constant evaluation just to make sure they were usable. Additive manufacturing changed that overnight. It gave engineers an immediate advantage: fewer defects, faster turnaround, and fewer parts to assemble. With DMLS [Direct Metal Laser Sintering], you could suddenly get much better material properties than castings. And you could go from a drawing to a finished product in a much faster timeframe.”
The benefits piled quickly. Complex geometries could be built as single, monolithic pieces instead of assemblies, cutting down on part count and boosting reliability. More importantly, fewer parts meant fewer failure points.
“Additive gave us a twofer right out of the gate. You could prototype faster, and you got better reliability because reliability is tied to part count.”
Test chamber for the HEX thruster. Image courtesy of Portal Space Systems.
When Thornburg took charge of developing the Raptor engine at SpaceX, using additive manufacturing was the obvious conclusion. The team had already tested it on Merlin engines, and the benefits were clear. The real hurdle was materials: some powders and alloys didn’t yet exist, so certain parts still had to be machined or cast. But the intent was to print as much as possible, as fast as possible.
“Elon wanted an engine in less than five years. We had one on the stand in four. Additive made that possible.”
The Dirty Room and the Dream
Of course, additive didn’t solve everything. Post-processing remained, and still remains, a reality. Thornburg remembers some experiences he’s had at sandblasting rooms and polishing labs he’s seen hidden away.
“There’s a lot of kabuki theater happening sometimes between selective pictures and the final part,” he says. If he could wave a magic wand, Thornburg knows what he’d ask for: “a true Star Trek replicator. Give me a part that comes out of the printer with the exact properties I need—no post-processing required. That’s the problem to solve.”
That’s the dream. The reality, Thornburg admits, is that additive still has boundaries, especially when it comes to size and metallurgy. Even with today’s advances, size limits keep engineers from printing everything.
“DMLS is very good up to a certain size, but rocket engines and nuclear components push the boundaries. Any defect at those pressures and temperatures just can’t be tolerated.”
That’s why process control (building each part exactly the same way) is still the deciding factor.
Vacuum chamber to test HEX thruster. Image courtesy of Portal Space Systems.
Printing in Space
Thornburg believes 3D printing won’t just transform Earth-based manufacturing; it will become essential in orbit and on other planets.
“You can’t pack everything you’ll need for Mars or the Moon,” he says. “It’s like a camping trip. Whatever you think you’ll need, you won’t. You’ll need the thing you left at home. Printers are the lifeline. Experiments on the ISS and ideas for recycling space junk into feedstock are just the start.”
At Portal Space Systems, 3D printing drives much of the company’s propulsion work. Some parts are printed in-house, while others are sourced from suppliers. Either way, it’s central to the company’s intellectual property. Additive is especially critical in the company’s solar-thermal propulsion system and several structural components across its spacecraft.
“More than a manufacturing choice, it’s part of Portal’s intellectual property. What we do wouldn’t be possible without additive manufacturing,” he says.
Jeff Thornburg and his team at Portal’s HQ.
Since 2011, Thornburg hasn’t worked anywhere that didn’t rely on 3D printing: “From SpaceX to Kuiper to Portal, it’s become part of the aerospace culture. I wouldn’t do any development project in aerospace without additive manufacturing.”
The engineer who once waited years for castings now pushes for a world where parts are printed, finished, and flown in days.
Images courtesy of Portal Space Systems
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