A new design for a plasma engine fuels on only thin air

Choosing an orbit for a satellite always comes with trade-offs. Very low Earth orbit (VLEO), between 100–450 km (62–280 miles), has distinct advantages. Remote-sensing cameras can take better pictures, communications and radar require less power, and atmospheric drag automatically cleans up dead satellites.

September 14, 2026 A new design for a plasma engine fuels on only thin air by Andy Tomaswick, Universe Today edited by Swati Mestri, reviewed by Andrew Zinin Swati Mestri Scientific Editor Meet our editorial team Behind our editorial process Andrew Zinin Chief Editor Meet our editorial team Behind our editorial process Editors' notes This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: fact-checked preprint trusted source proofread The GIST Add as preferred source Fully Assembled RF Helicon-based Plasma Thruster. But there is also a cost—air friction requires satellites in this orbit to use an engine nearly constantly to stay aloft, which in turn requires fuel—typically expensive gases like xenon.

So, as part of his Ph.D. Thesis at the University of Stuttgart, available on arXiv, Francesco Romano decided to solve that problem by using the air molecules that cause the friction as fuel for a plasma engine to keep satellites aloft indefinitely in VLEO. His solution falls into a category of atmosphere-breathing electric propulsion (ABEP) systems.

These scoop up thin air in front of a spacecraft (or, in some cases, a missile) and channel it into an electric engine, which then turns the molecules into plasma and shoots it out the back, producing thrust. It's easy enough to explain in theory, but in practice, there are difficult technical problems to work around. The first is atomic oxygen (AO).

In the upper atmosphere, UV radiation splits O 2 into this aggressive, single-atom form of the gas that we all need to breathe. AO is notoriously oxidative, corroding metal electrodes, acceleration grids and even the cathodes used in standard Hall thrusters or other types of ion engines.

Fraser goes into details about ion engines. Without that feature, the whole ion-propulsion system fails.

Another difficult feature when designing engines for use in VLEO is the variability of the atmosphere itself. It changes based on the day-night cycle, latitude and even solar activity.

Making sure an engine can continually operate in all these different conditions has proven difficult so far. To solve these problems, Romano developed a contactless, neutralizer-less radio-frequency (RF) helicon plasma thruster and paired it with an optimized atmospheric intake system.

Let's tackle the intake system first. He tested three different versions of an intake.

One, called an "enhanced funnel design," acted as a molecular trap to capture air particles that are spread so far apart that they never run into each other. Next, he used a "diffuse intake" with a compact hexagonal design made of a coated titanium alloy.

Finally, he designed what he called a specular intake, a parabolic mirror coated with graphite or silicon dioxide that bounced particles directly into the engine. Detailed look at the Birdcage antenna, inspired by MRI machines.

Romano The clear winner, both in terms of collection efficiency and alignment sensitivity, was the specular intake. It collected about 94.3% of air particles (AO, argon or nitrogen in a wind tunnel test), and the efficiency dropped only 8% when subjected to a 15° tilt.

To design the thruster, Romano turned to a medical device for inspiration. Using a birdcage antenna, similar to those used in MRIs, he designed a thruster that ensured 99% of the delivered electrical power entered the thruster.