It sounds like NASA pipe dream: a new spacecraft engine that is 40 percent more energy efficient than today. Moreover, its fuel costs less than a thousandth and weighs one-eighth of its mass. A startup called Orbital arc claims to be able to create such an engine.
With this design, “we can go from a motor that's about a few inches across and weighs a few kilograms to a motor-on-a-chip that's about an inch in diameter and has the same thrust power but weighs about eight times less,” the company founder said. Jonathan Huffmanspeaks.
The hardware will be small enough to fit into the smallest low-Earth orbit, according to Orbital Arc. satellites but generate enough energy for an interplanetary mission. Such low-cost traction could bring significant savings for satellite operators hope to avoid debrisor mission operators seeking to send probes to distant planets.
The key to these innovations is the combination of cheap, readily available fuel, MEMS microprocessingand strong love for Science fiction.
Designing a Better Engine
Engines usually work by creating and then releasing plasmapushing the spaceship in the opposite direction. Always popular inside Hall thrustersmagnetic field traps electrons in a narrow circular orbit. The noble gas (usually xenon) drifts into a narrow channel, where it collides with the circulating charge, knocking out electrons and ionizing it into plasma. High voltage electric field then rockets plasma comes out of the exhaust.
Orbital Arc technology looks a little different and came about almost by accident. Huffman was a biotechnology consultant and self-described “sci-fi nerd” tasked with developing fictional technology for a futuristic video game in his spare time. He needed to figure out how planes would be able to maneuver in 250 years to make the game's controls realistic, so he began researching modern propulsion systems.
He quickly came to understand the limitations of existing ion engines, which he believed could be improved in the coming centuries, and (spoiler alert) perhaps sooner: if a mission requires more thrust, its engine must be heavier. But most importantly, “there is a certain point where adding engine mass negates any benefit that can be gained from the extra thrust,” he says. So, to maintain these benefits, engines must be small but powerful.
Huffman's exposure to biological laboratories gave him an unexpected advantage when it came to engine design. Through his work, he learned about nanoscale tips—ion-emitting nozzles—used to generate intense electromagnetic fields for biomedical research. They can be found in mass spectrometers, instruments that identify unknown chemicals by turning them into ions, accelerating them and watching them fly.
He suspected that such a system could be further miniaturized to accommodate the ionization process in the engine. After a year and a half of developing the concept, Huffman was convinced that his small engine idea had potential beyond a video game.
And he was right. At the heart of each Orbital Arc engine is a chip with millions of micrometer-sized, positively charged tips built into it that direct the flow of gas, sending naphthalene in and ions flowing out.
When naphthalene molecules pass through the charged tips, the molecules become polarized – in this case, this means that the electrons of the molecule are collected on one of its sides. Due to the uneven field created by the charge, the molecules are attracted to the tip and then remain there, unable to escape until they release electrons.
Once they release electrons, “you have an ion that's on the tip of a really sharp, positively charged object, and it's now positively charged. So it accelerates,” Huffman explains. The repelled ions fly by and splash out into space, pushing the spacecraft forward.
According to Huffman, the advantage of this design is energy savings by eliminating the internal plasma generation that other engines rely on. “Plasma is wasted because everything is mixed in one big soup,” Huffman explains. Free electrons in the plasma can recombine with ions to form neutral atoms, “and now I've lost the energy I put into creating this charged particle. It's a waste of energy.” Recent calculations show that a motor with a naphthalene nanotip provides a performance improvement of 30 to 40 percent. energy efficiencyhe claims.
By eliminating plasma entirely, the Orbital Arc design can benefit from energy savings, as demonstrated in a recent demonstration. In a recent test, just six Orbital Arc tips were able to generate approximately three times more ion current than an array of 320,000 tips from the group of WITHsays Huffman.
Two and a half years after his “aha” moment (and after he “created the whole damn thing in Excel”), Huffman became CEO of Orbital Arc, a startup testing four working prototypes of its tiny chips.
The engine is innovative not only in its size, but also in terms of fuel. Naphthalene is the main ingredient mothballs– is a readily available by-product of oil refineries. The compound may smell bad, but it is safe to handle and extremely cheap, says Huffman, costing about $1.50 per kilogram, compared with about $3,000 per kilogram for xenon.
Use of naphthalene in Orbital Arc AIDS in reducing production costs, which the company claims is one percent of the cost of traditional Hall motors. “I think it's plausible,” he says Jonathan MacArthurpostdoctoral researcher at Princeton University Electric traction and Plasma Dynamics Laboratory. “What remains to be seen is that, okay, it's cheap, but if I put diesel in my gas car because it's on sale doesn't necessarily bode well for my car's engine.” He'd like the startup to publish data to back up its cost claims, and while it's at it, also data to back up its performance claims.
From prototype to flight
Currently in the prototype stage, each chip contains only six tips, manufactured using MEMS manufacturing processes in a clean room at the factory. Oak Ridge National Laboratory. But the next step will be to produce a full-scale version of the chip in a university lab, Huffman says.
The company will then need to build a motor that rotates around the chip. “It's a relatively simple device. It's a valve, a few wires and a few structural components. Very, very simple,” says Huffman. He says he will need to integrate all these parts before doing vibration testing. radiation testing, thermal cycling and other stages on the way to obtaining flight qualifications. “In two years, I’ll probably have a product that will sell.”
Huffman believes Orbital Arc's first customers will be small teams such as startups or research groups. He is confident they will be willing to try the new engines, despite the risks inherent in new technologies, due to the expected performance at a low price. “So some people will have no choice but to buy it, even if it hasn't flown yet. If they want to accomplish the mission, they'll take the risk,” he says.
Princeton's MacArthur is skeptical of this claim. “When you choose a propulsion system, data and heritage are usually everything.” He's not sure customers would be willing to take the risk of purchasing a new engine with no flight history.
However, some CubeSat-sized missions may agree to use the new engines at a discount, suggests Oliver Chia-Richardswho studies space propulsion at the University of Michigan. Customers may also be willing to take a chance on Orbital Arc because other startups such as compulsionhave recently achieved success with their new electric propulsion technology, he says. But “there are always risks with these things.”
By targeting smaller missions, Huffman wants to “build something that we can show off a little bit.” He notes that to date, no satellite has made a round trip to Earth. moon after a year in Earth orbit without refueling. It depends on funding, and more attractive opportunities may emerge, “so we'll see,” he says.
And he doesn't stop there. “We're tapping into mathematical reality,” Huffman says. “If you cut off the dry mass of a spacecraft, you'll get an exponential gain in its performance because of the way the rocket equation works. You'll be penalized exponentially for the extra dry mass.”
By integrating Orbital Arc engines, the mission can reduce the mass of solar panels and power supplies because their drive is more energy efficient, reduce the mass of the tank because mothballs do not require a pressure vessel like xenon, and reduce the mass of the engine itself, he said. With these savings, “you'll go from one-way science missions to Mars to flights with two-way manned flight in Jupiter without refueling,” says Huffman.
So while the engine is Orbital Arc's first step, Huffman envisions the next one being an ultra-light space bus, long before the far-future era that inspired his video games.
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