Satellites need propulsion to hold their position or move around in space. Conventionally, satellites use rocket-like chemical propulsion, but electrical thrusters are becoming increasingly popular due to their better efficiency. However, current electrical propulsion systems still need to use a propellant, such as xenon, and their mission lengths are therefore limited by how much propellant they can carry. Due to weight constraints, satellites can carry only a limited amount.
Those orbiting close to the Earth, in the range of a few hundred kilometers (about 125 miles), consume it at a higher rate, as they need to compensate for the atmospheric drag that slows them down and pulls them toward the Earth.
Instead of carrying its own propellant, a satellite using ESA's new system would skim air molecules from the top of Earth's atmosphere. The molecules turn into plasma when compressed. An electric field is then used to accelerate the stream of plasma to provide thrust for the satellite.
[Earth's Colorful Atmospheric Layers Photographed from Space]
"Providing atmospheric drag compensation without the use of carry-on propellant, this kind of electric propulsion would let satellites orbit at very low altitudes around Earth for very long operational time," Louis Walpot, who leads the project at ESA, told Space.com in an email.
"Normally their orbit would decay rapidly and they'd reenter the atmosphere," Walpot said.
Together with the thruster, ESA tested an innovative collector that captures incoming air as it hits the thruster at the staggering orbital speeds of about 4.9 miles per second (7.8 kilometers per second). The collector strips nitrogen and oxygen molecules from the air and turns them into fuel. It's this collector that makes the system the first of its kind, demonstrating how an air-breathing thruster would actually work in orbit.
"This design of the collector was challenging because the air molecules tend to bounce out again, rather than be retained and compressed to a point where they turn into plasma, capable of being accelerated with an electric field," Walpot said. "The collector-plus-thruster design is entirely passive in nature — the air enters the collector due to the spacecraft's velocity as it orbits around Earth. All it needs is electric power to ionize the compressed air."