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: 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. 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 O2 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.
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, 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.
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