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.
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