ESA's new thruster uses air as fuel

Researchers have designed a rocket thruster that uses air instead of fuel, which could change how satellites fly in the lowest orbits around Earth.

The new thruster can collect, compress, electrically charge and then release air molecules, eliminating the need for chemical fuel. Only some electricity is needed, which can usually be harvested from the Sun.

According to the lab tests run on the ground by the team from the European Space Agency (ESA) behind the project, the new thruster could power "a new class of satellites", operating for years around planets such as Earth or Mars.

"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," says one of the ESA scientists, Louis Walpot.

The ESA has been working on the project for over a  decade, with its GOCE gravity mapper satellite which  ran for over five years using a similar type of thruster. It however relied on 40 kilograms (88 pounds) of xenon as a propellant to keep it going.

But the agency has worked out how to use air and though there are no air molecules out in the vacuum of space, low orbits can provide enough of them to a satellite a periodic boost.

The researchers conducted tests on the new machine in a vacuum chamber. A stream of xenon was first used and then a xenon-air mixture.

''When the engine exhaust plume changed from the characteristic blue of xenon to purple, we knew we had succeeded,'' said Walpot.

''We finally relighted the system several times with only atmospheric fuel to demonstrate the feasibility of the concept,'' said Walpot. The air was not very dence and sent at very high speed to simulate the conditions encountered by a satellite flying at more than 125 miles of altitude. ''This result shows that electric propulsion using air is no longer in the realm of theory, but that it is indeed a tangible operational concept, ready to be developed and that can one day be used to define missions of a new kind,'' he added.