It sounds like a NASA pipe dream: a new spacecraft thruster that’s up to 40 percent more power efficient than today’s. Even better, its fuel costs less than a thousandth as much and weighs an eighth of the mass. A startup called Orbital Arc claims it can make such a thruster.

With this design, “we can go from a thruster that’s about a few inches across and several kilograms to a thruster on a chip that’s about an inch across and has the same thrust output, but weighs about an eighth as much,” the company’s founder, Jonathan Huffman, says.

According to Orbital Arc the hardware would be small enough to fit on the smallest low-earth orbit satellites but generate enough power for an interplanetary mission. Such inexpensive thrust could bring meaningful savings for satellite operators hoping to dodge debris, or mission operators aiming to send probes to distant planets.

The key to these innovations is a combination of cheap, readily available fuel, MEMS microfabrication, and a strong love of sci-fi.

Designing a Better Thruster

Thrusters generally work by creating and then expelling a plasma, pushing a spacecraft in the opposite direction. Inside ever-popular Hall thrusters, a magnetic field traps electrons in a tight, circular orbit. A noble gas—commonly xenon—drifts into a narrow channel where it collides with the circulating charge knocking off electrons and ionizing it into plasma. A high-voltage electric field then rockets the plasma out the exhaust.

Orbital Arc’s technology looks a bit different and came about almost coincidentally. Huffman was a biotech consultant and self-described “sci-fi nerd” who, in his spare time, had been commissioned to design fictitious technology for a futuristic video game. He had to figure out how aircraft might maneuver 250 years from now to make the game controls realistic, and so he started researching state-of-the-art propulsion systems.

He quickly came to understand a limitation of existing ion thrusters he thought could be improved upon within the coming centuries, and (spoiler alert) possibly sooner: if a mission requires more thrust, its thruster needs to be heavier. But crucially, “there’s a certain point at which adding more mass to the thruster negates all of the benefits you can get from extra thrust,” he says. So, to retain those benefits, thrusters need to be small but mighty.

Huffman’s familiarity with biology labs gave him an unexpected edge when it came to propulsion design. Through his job, he learned about nanoscale tips—nozzles that emit ions—used to generate intense electromagnetic fields for biomedical research. They’re found in mass spectrometers, instruments that identify unknown chemicals by converting them into ions, accelerating them, and watching how they fly.

He suspected that such a system could be miniaturized even more to make the ionization process in a thruster. After a year and a half of developing the concept, Huffman was convinced that his idea for a small thruster had potential beyond a video game.

And he was right. Each Orbital Arc thruster has a chip at its heart with millions of micrometer-scale, positively charged tips embedded in it and channels to direct gas flow—naphthalene flows in, and ions flow out.

As naphthalene molecules pass the charged tips, the molecules** **become polarized—here, that means a molecule’s electrons bunch up on one of its sides. Because of the uneven field created by the charge, the molecules get dragged towards a tip and are then trapped there, unable to escape until they release electrons.

Once they release electrons, “you have an ion that’s at the point of a really sharp positively charged object, and it itself is now positively charged. So it accelerates,” Huffman explains. The repelled ions fly by and spray out into space, propelling the spacecraft forward.

An advantage of this design is the power savings that come from avoiding the internal plasma generation that other thrusters rely on, Huffman says. “Plasmas have losses because everything’s in a big soup mixed together,” Huffman explains. Free electrons in a plasma can recombine with ions to produce neutral atoms “and now I’ve lost the energy that I put in to make that charged particle. It’s a waste of power.” Recent calculations show the naphthalene nanotip thruster providing a 30 to 40 percent improvement in power efficiency, he claims.

By avoiding plasmas all together, the Orbital Arc design is able to capitalize on the power savings, as shown in a recent demonstration. In a recent test, just six of Orbital Arc’s tips were able to generate about three times more ion current than an array of 320,000 tips from a group from MIT, Huffman says.

Two and a half years after his “aha” moment (and after “building the whole darn thing in Excel”), Huffman is the CEO of Orbital Arc, a startup testing four working prototypes of its tiny tips-on-chips.

The thruster is not only innovative for its size, but also for its fuel. Naphthalene—the main ingredient of mothballs—is a readily available byproduct of oil refineries. The compound may smell bad, but it’s safe to handle and extremely cheap, Huffman says, costing around US $1.50 per kilogram compared to some $3,000 per kilogram for xenon.

Orbital Arc’s use of naphthalene aids in their shrinking of product costs, which the company claims is at one percent of traditional Hall thrusters. “I think that’s believable,” says Jonathan MacArthur, a postdoctoral researcher at Princeton University’s Electric Propulsion and Plasma Dynamics Laboratory. “What remains to be seen is, okay, it’s cheap, but if I put diesel in my gas car because it’s on sale, that doesn’t necessarily bode well for the engine in my car.” He wishes the startup would release data to back up their cost claims—and while they’re at it, data to back up performance claims, as well.

From Prototype to Flight

For now, in the prototype stage, each chip contains only six tips, fabricated using MEMS manufacturing processes in a cleanroom at Oak Ridge National Laboratory. But the next step is to manufacture a full-scale version of the chip in a university lab, Huffman says.

Then, the company will need to build the thruster that goes around the chip. “That’s a relatively simple device. It’s a valve, it’s a few wires, it’s a few structural components. Very, very straightforward,” Huffman claims. He says he’ll need to integrate all of those parts before running through vibration testing, radiation testing, thermal cycling, and other steps on the way to achieve flight qualification. “Two years from now, I can have a product that is sellable, probably.”

Huffman thinks Orbital Arc’s initial customers would be small teams, like startups or research groups. He’s confident that they’ll be willing to try the new thrusters, despite the risks inherent to new technologies, because of the expected performance at low cost. “So some folks just won’t have any choice but to buy it, even if it hasn’t flown before. If they want to do the mission, they’re going to take the risk,” he says.

Princeton’s MacArthur is skeptical of that claim. “When you’re choosing a propulsion system, generally data and heritage is everything.” He’s not so sure that customers will be willing to take on the risk of a new thruster without a history of flight.

Still, some CubeSat-scale missions may agree to use new thrusters at a discount, suggests Oliver Jia-Richards, who studies in-space propulsion at the University of Michigan. Customers may also be willing to take a chance on Orbital Arc because other startups, like Enpulsion, have been recently successful with their new electric propulsion technology, he says. But “with this kind of thing, there’s always risks.”

After targeting small missions, Huffman wants to “build something where we show off a bit.” He notes that, as of yet, no satellite has completed a round trip to the moon after a year in Earth’s orbit without refueling. It’s funding dependent and there may be more attractive opportunities that come up, “so we’ll see,” he says.

And he’s not stopping there. “We are tapping into a mathematical reality,” Huffman says. “If you cut dry mass off of spacecraft, you gain exponential benefits in its performance because of the way the rocket equation works. You get exponentially penalized for extra dry mass.”

By integrating Orbital Arc’s thrusters, he says, a mission could cut solar panel and power supply mass because it drive is more power efficient, cut tank mass because naphthalene doesn’t require a pressure vessel unlike xenon, and cut thruster mass itself. With these savings, “you go from flying one-way science missions to Mars to flying two-way human rated missions to Jupiter without refueling,” Huffman claims.

So while the thruster is Orbital Arc’s first step, Huffman envisions an ultra-light spacecraft bus next—arriving long before the far-future era of the video game that inspired it.