How to make atmospheric drag work for satellites, instead of against them.
Concept art of air-breathing satellite. Image: ESA–A. Di Giacomo
In the near future, Earth orbit may be filled with satellites that generate thrust out of thin air. This novel concept of air-breathing spacecraft is in the works at the European Space Agency (ESA), and it could drastically increase the lifespan of satellites in low-altitude orbits around Earth, and even other planets like Mars.
The method, known as air-breathing electric propulsion (ABEP) or RAM electrical propulsion, has been speculated about for over a decade. But on Monday, ESA announced that it successfully fired up a prototype thruster in a vacuum chamber that simulates low Earth orbit, marking the first laboratory demonstration of the technology’s principles. The thruster air intake parts were designed by the Polish company QuinteScience, while the prototype was built by the Italian company Sitael.
“This project began with a novel design to scoop up air molecules as propellant from the top of Earth’s atmosphere at around 200 kilometers (124 miles) altitude with a typical speed of 7.8 km/s,” said Louis Walpot, an ESA aerospace engineer, in a statement. “The team ran computer simulations on particle behaviour to model all the different intake options but it all came down to this practical test to know if the combined intake and thruster would work together or not.”
The thruster is pretty simple for a spacecraft propulsion system: High-speed air molecules are collected from the atmosphere, compressed by interior coils, charged by electrodes, and spat out the back to accelerate the craft.
The idea, if successfully implemented, would solve several orbital headaches in one fell swoop. Low-altitude orbits, which remain within the boundaries of the atmosphere, are a literal drag on spacecraft. Atmospheric air resistance necessitates that low-Earth orbit spacecraft, like the International Space Station (ISS), are equipped with extra fuel, so that they can regularly boost themselves into their operational trajectories (otherwise, they would succumb to orbital decay and burn up in re-entry).
But an air-breathing satellite would turn planetary atmospheres into a propulsive resource, rather than an expenditure. Instead of ending missions when a satellite’s propellant runs out—which normally takes a few years—air-breathing satellites would have much longer lifespans. Now that ESA has produced a working version of these efficient engines, it might not be too long before the low-Earth orbit is graced with satellites that use air to help power themselves, just like we do.
“This result means air-breathing electric propulsion is no longer simply a theory but a tangible, working concept, ready to be developed, to serve one day as the basis of a new class of missions,” Walpot said.
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