The European Space Agency (ESA) has successfully tested a prototype ion engine powered by air that could provide propulsion for orbiting satellites almost indefinitely, and could even help power future missions to Mars.

Satellites in orbit traditionally use an onboard propellant — usually xenon — to adjust their orientation and keep their orbit from decaying. Their life is limited by how much propellant they can carry, however. The new “air breathing” design skims molecules from the upper atmosphere and converts them into useable fuel.

In conjunction with the space agency Sitael, the test was conducted in a vacuum chamber in Italy to simulate an altitude of approximately 125 miles. “This project began with a novel design to scoop up air molecules as propellant from the top of Earth’s atmosphere,” said Louis Walpot of the ESA in the announcement.

There are no moving parts on the thruster — all it needs is electricity for the coils and electrodes. Although electricity is plentiful in space, either from solar panels or nuclear decay, it can’t provide thrust.

The electric field is used to compress the air and then accelerate the stream of plasma created. “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,” Walpot told Space.com. “Normally their orbit would decay rapidly and they’d reenter the atmosphere.”

A new collector intake created by QuinteScience in Poland gathers air molecules as the engine travels through space at nearly five miles per second, and Sitael designed a dual-stage thruster to charge and accelerate the incoming air. “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,” Walpot explained. “All it needs is electric power to ionize the compressed air.”

The basic Hall thruster design is not new, but the test results using nitrogen and oxygen proved the collector could work on actual space missions. “When the xenon-based blue colour of the engine plume changed to purple, we knew we’d succeeded,” Walpot said.

Because the atmosphere on Mars is not nearly as dense, a spacecraft would need to reduce its altitude to 75 miles or less to scoop up carbon dioxide, which could also be used as fuel.

“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 added.