New Plasma Thruster Uses Atmospheric Gas to Keep Satellites in Orbit Indefinitely
Satellite Atmosphere-Breathing Electric Propulsion Engine Design Evaluated
A proposed satellite propulsion system designed to capture and use extremely thin atmospheric gases as fuel in Very Low Earth Orbit (VLEO) has demonstrated high collection and operational efficiencies in laboratory testing and computational models, according to research published on arXiv by Francesco Romano from the University of Stuttgart. While the concept addresses the severe drag penalties of operating at altitudes between 100 and 450 kilometers, researchers emphasize that the technology remains unproven on an actual orbital mission.
The Tech TL;DR:
- Propulsion Breakthrough: Francesco Romano’s PhD research models an atmosphere-breathing electric propulsion (ABEP) system that converts ambient VLEO air into a plasma jet to maintain orbit without carrying a conventional xenon propellant supply.
- Intake Efficiency: Lab evaluations tested enhanced funnels, diffuse hexagonal titanium arrays, and specular parabolic mirrors, identifying a graphite- or silicon dioxide-coated specular intake that captured roughly 94.3% of incoming test molecules with minimal loss during a 15-degree tilt.
- Neutralizer-Free RF Thruster: Inspired by medical device hardware, a birdcage antenna design channels roughly 99% of delivered electrical power into the system, operating on 50-60W of RF power while using a magnetic solenoid to expel a quasi-neutral plasma stream.
Engineering Challenges in Very Low Earth Orbit
Operating spacecraft in VLEO offers distinct operational advantages, including sharper images from remote sensing cameras and reduced power requirements for communications and radar systems. Atmospheric drag also serves as a natural disposal mechanism for inactive satellites. However, that same drag creates a significant engineering hurdle. Air resistance continually slows spacecraft down, demanding nearly continuous thrust to prevent orbital decay.
Conventional propulsion systems solve this problem by carrying onboard propellant, typically costly gases like xenon. ABEP systems eliminate this mass penalty by ingesting ambient atmospheric molecules and ionizing them to generate continuous thrust. Building a functional ABEP system requires overcoming two primary obstacles: extreme chemical corrosion caused by the upper atmosphere and variability across solar cycles, latitude, and day-night transitions.
At VLEO altitudes, ultraviolet solar radiation splits O2 molecules into atomic oxygen (AO). Single-atom oxygen is highly oxidative, rapidly corroding metal electrodes, acceleration grids, and standard cathodes used in Hall thrusters or other types of ion engines. In traditional electric propulsion architectures, the cathode acts as an electron gun that neutralizes the spacecraft. Without neutralization, the entire spacecraft becomes charged and simply sucks the charged particles right back to itself, nullifying any net thrust. AO rapidly destroys these essential cathodes, causing system failure.
Specular Intake Design and RF Plasma Generation
To capture sparse air molecules before they collide with the spacecraft structure, Romano evaluated three distinct intake configurations during his research at the University of Stuttgart. The tested geometries included an enhanced funnel design acting as a molecular trap, a diffuse intake utilizing a compact hexagonal array made from a coated titanium alloy, and a specular intake built from a parabolic mirror coated with either graphite or silicon dioxide.
Laboratory wind tunnel trials identified the specular intake as the superior design. The parabolic mirror configuration successfully collected approximately 94.3% of incoming test particles—consisting of atomic oxygen, argon, and nitrogen—and maintained performance with only an 8% drop in efficiency when subjected to a 15-degree tilt.
To eliminate the vulnerable cathode neutralizer entirely, Romano adapted antenna designs commonly found in medical magnetic resonance imaging (MRI) equipment. By implementing a birdcage antenna configuration, the thruster achieved an electrical power transfer efficiency of roughly 99%, avoiding the resistive power losses typical of standard wire coils. A solenoid wrapping the engine applies a magnetic field that expels both positive and negative ions simultaneously in a quasi-neutral plasma jet.
Vacuum chamber tests simulating VLEO gas concentrations demonstrated that the helicon-based plasma thruster could generate steady streams of plasma using just 50 to 60 watts of radio-frequency power. This power draw falls well within the generation capacity of traditional spacecraft solar panels, making the architecture viable for long-duration missions if deployment hurdles are cleared.
Future Deployment Realities and System Validation
Following experimental vacuum validation, the research applied numerical models to simulate real-world VLEO operational profiles.