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New Satellite Engine Could Use Earth's Atmosphere to Stay in Orbit Indefinitely
A satellite engine that uses atmospheric gases as fuel shows promise in laboratory tests and modeling, but its performance on a mission remains unproven.
Choosing an orbit for a satellite involves balancing benefits and drawbacks. Very Low Earth Orbit (VLEO), which spans roughly 100 to 450 km (62 to 280 miles) above Earth, offers several advantages. Remote sensing cameras can capture sharper images, communications and radar systems need less power, and atmospheric drag helps remove inactive satellites from orbit naturally.
That same atmosphere also creates a major challenge. Even at these altitudes, air resistance slows spacecraft down, so satellites must produce thrust almost continuously to remain in orbit. Conventional propulsion systems require onboard fuel, often costly gases such as xenon.
As part of his PhD research at the University of Stuttgart, published on arXiv, Francesco Romano explored a different approach. His concept uses the atmospheric molecules responsible for drag as fuel for a plasma engine, potentially allowing satellites to remain in VLEO indefinitely without carrying a conventional supply of propellant.
The technology belongs to a class known as atmosphere-breathing electric propulsion (ABEP). These systems collect the extremely thin air in front of a spacecraft (or, in some cases, a missile) and direct it into an electric engine. The engine converts the incoming molecules into plasma and expels it from the rear to generate thrust.
The basic idea is straightforward, but turning it into a practical propulsion system requires solving several difficult engineering problems.
First is atomic oxygen (AO). In the upper atmosphere, UV radiation splits O2 into this aggressive, single atomic 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.
Perhaps most importantly, AO burns through the cathodes used in the “electron gun” that neutralizes the spacecraft so that the whole thing doesn’t become charged and simply suck the charged particles right back to itself, nullifying the thrust they provide. 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, the 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.